As for a Morgana redemption arc? She might not need one if the writers let her complete her Heroine’s Journey.

If the writers wanted, it would be relatively easy to do. After experiencing a physical death, Morgan should experience a spiritual one. When she does she can resume a Heronine's Journey that's been occurring since Season 1 Ep. 1.

If any feminist read this, this was taken from link and link and this was taken from Psychology for Screenwriters by William Indick which was distilled from The Heroine's Journey by Maureen Murdock using feminist anthropological interpretations of primitive societies including the works and theories of Margaret Meade. And for my own sanity, I’ll use Hero with a male pronoun (his) and Heroine with a female one (her).

The Murdock work in turn was a response to the work of her former teacher, The Hero’s Journey by Joseph Campbell, under the premise that all societies shared basic, fundamental notions called Archetypes which could be outlined in stages showing that across all cultures the same story was told through the mask of that culture making “universal truths” accessible to that society. However, where the Hero’s Journey involved obtaining the boon (the purpose of the quest, like the Cup of Life) using the masculine aspects of personality (Animus), the Heroine’s Journey involved using the feminine aspects of personality (Anima) and realizing that the boon of the Hero was often illusory because the actual purpose of the Myth was a reconciliation between the Animus and Anima.

It is important to remember that: 1) the Stages in either the Hero’s or Heroine’s Journey can occur either literally (concretely) or figuratively (abstractly); 2) the Hero could be either male (like Merlin/Arthur) or female (like Lara Croft) in this journey; and 3) the protagonist in the Heroine’s Journey could be a female (like Erin Brockavich) or male (like Daniel Kaffee in A FEW GOOD MEN). Finally as Indick pointed out the Hero’s Journey was all about achieving legendary status after death while the Heroine's journey was about achieving psychological stability in life.

The Hero’s Journey

Stage 1: Departure: The hero is called to adventure, although he is reluctant to accept. (Season 1)
Stage 2: Initiation: The hero crosses a threshold into a new, more dangerous world, gaining a more mature perspective. (Season 2)
Stage 3: The Road of Trials: The hero is given supernatural aid, endures tests of strength, resourcefulness, and endurance. (Season 3)
Stage 4: The Innermost Cave: The hero faces a great trial. It is a period of undoing, and change. Because of this trial, the hero is reborn in some way—
physically, emotionally, or spiritually. Through this experience, the hero changes internally. (Season 4)
Stage 5: Return and Reintegration with Society: The hero uses his new wisdom to restore the land of Albion (Season 5?)

The Heroine’s Journey

Stage 1: SEPARATION FROM THE FEMININE: The rejection of typically female values, the Mother Goddess, and female archetype. (Beginning in Season 1 Episode 1, during her refusal to join the celebration and later challenging Uther in To Kill the King)

Stage 2: IDENTIFICATION WITH THE MASCULINE & GATHERING OF ALLIES: The heroine finds a Mentor (the wise old man) to guide her through the male dominated world who initiates her into her new realm or masculine combat or contests. (Seen as early as Season 1 on meeting Merlin, Mordred, the Druids).

Stage 3: ROAD OF TRIALS, MEETING OGRES & DRAGONS & FALSE KNIGHTS : A series of trials in which she must integrate the masculine qualities needed to complete her quest by internalizing traditionally male strengths and slaying of male monster archetypes:

# Two-headed Dragon of Dependency - conflicting needs of her endeavor and family must be 'slain' through finding a balance between them. (Initially, the Druids and her place in Camelot; later, her desire for the Throne and her familial loyalty to Arthur and Uther)
# Ogre, the Tyrant of Inferiority - The inner tyrant of 'success at all costs' must be won over while also the outer tyrant must be defeated (the corporation, the system, injustice) there is no point in doing one without the other - again the art of balance is stressed. (Uther)
# Knight in shining Armour - The illusion of the person who will solve all her problems must be seen through and dispatched; otherwise, she returns to being a maiden in distress (Morgause and Cenred, later Agravaine, Helios)

Stage 4: FINDING THE ILLUSORY BOON OF SUCCESS: At the highpoint of her struggle she may feel like she has won it all by becoming Queen but she learns that it is easier to judge how to rule than to actually rule. Morgana obtains her goal of her quest but this is illusory because this alone does not return the old religion and make the land safe for magic. Instead, she is hated and it seems so is magic. (The Coming of Arthur and the Sword in the Stone)

Stage 5: PHYSICAL AND SPIRITUAL ARIDITY: DEATH

And in the end, Morgana dies but is saved by Aithusa (the Light of Day) because her Journey is not yet done. She has found the boon of success to be a fraud and questions her purpose and goals. Once her mission has been reaffirmed, she would perform her quest with renewed vigor by seeking the way to achieve the true boon of the quest which Acceptance of Magic in the Land.

This would occur in what Murdock refers to as Stage 6: INITIATION & DESCENT TO THE GODDESS. Stage 7: URGENT YEARNING TO RECONNECT WITH THE FEMININE. Stage 8: HEALING THE MOTHER/DAUGHTER SPLIT. Stage 9: HEALING THE WOUNDED MASCULINE/FINDING THE HEART OF THE INNER MAN. Stage 10: INTEGRATION OF MASCULINE & FEMININE.

Fitting that into an episode we'd outline it as follows: Stage 1: Departure: Morgana is called to adventure though she might be reluctant. Stage 2: Initiation: Morgana crosses a threshold into a new, more dangerous world, gaining a more mature perspective. Stage 3: The Road of Trials: Morgana with Merlin’s aid (or other Supernatural guide) endures tests of strength, resourcefulness, and endurance as she overcomes myths of inferiority, dependency, and romantic love. Stage 4: The Innermost Cave: Morgana faces a great trial against some aspect of the Triple Goddess and changes physically, emotionally, or spiritually as she accepts and integrates the old wisdom with the new. Stage 5: Return and Reintegration with Society: Morgana uses this new wisdom to help restore the land of Albion. She returns to Camelot to discover a different Arthur who has become more tolerant, nurturing, and sensitive while still being at the core, Arthur.

EXAMPLE: A concrete example of this:

Morgana sees a reflection of herself in a mirror and sees it transform into Uther Pendragon and then into a beggar raising questions about her claim to the throne of Camelot. She battles Arthur and Merlin for information and discovers that those she claims to help are being hurt. She discovers other information but it is unsettling provoking even more questions. And she must know the truth. She ventures into a quest with a reluctant Merlin/Arthur.

Along the way, Morgana and Merlin/Arthur face the Ogre of Inferiority, the Dragon of Dependency, and the Knight of Romantic Love who would side-track the quest (such as ghosts or memories of Uther, Morgause, and Agravaine). After overcoming these obstacles, Morgana and Merlin/Arthur meet the Triple God/Goddess, who imparts upon them knowledge where they see Uther in a different light.

Uther is the good and honorable man they never truly knew. He is the Uther who was not warped by hatred and fear of magic but the Uther who accepted and loved those who aided his kingdom with their gifts. She sees Uther and his friendship with Gorlois. This benevolent Uther who faced a dilemma which cost Gorlois his life but where there was no true betrayal except by a False Knight. This benevolent Uther changes because of magic gone wrong in the death of his friend (Gorlois) and the birth of his son (Arthur). This Uther was damaged because he lost those he loved most. And Arthur knows that not all who practice magic are evil.

And, from this, Morgana sees another side of Uther. Her hatred of him changes. She comes to understand how and why he acted as he did, even his reluctance to recognize her as his daughter (maybe upon his death Uther planned to give her her own kingdom to rule?). With this knowledge, Morgana feels shame, then guilt for causing the death of her father.

Morgana and Arthur realize that there is a difference between those who practice magic for evil and those for love. They return to Camelot and in time Morgana aids Merlin and Arthur, restoring magic to the land and becoming Morgana the Healer while Arthur becomes tolerant of magic.

Morgana becomes more like she was at the beginning (good-hearted and caring) and adopts Mordred as her son. He will in time betray Arthur and will try to kill Merlin in vengeance for his past encounter in S02E03.

Mordred reveals to all that he was the true Nemesis, the Enemy and Mastermind who manipulated Morgana. He fights them all but dies. Arthur is mortally wounded. Morgana tries to heal him to no avail. Before he dies, Merlin reveals that he and Arthur both have magic but Arthur must have faith in his belief. Arthur does and is brought back to life. Morgana takes him to Avalon to complete his recovery and return when Britain needs him.

In this way, Morgana the Healer is born and redeemed as part of the Eternal Cycle of Birth, Life, Death, and Resurrection, by helping in the creation of Albion and caring for the once and future king.

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Thoughts?

No one wants to see a Morgana redemption arc.

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Morgana doesn't seem to have any introspection, remorse or contrition or an ability for self-reflection. She is a "blinkered" obsessive-compulsive who will harm the very ones she claims to protect:

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It is doubtful if she will ever question her right to the throne or provide a plausible reason. Even Queen Annis looked at Morgana skeptically when she claimed the throne was hers. Something which most fans are dubious of:

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So, while Morgana COULD be redeemed; hopefully, she isn't and the writers leave her as the misbegotten child of Uther.

But, who knows? After George Lucas publish Star Wars I-III, Darth Vader was redeemed and became the hero of Star Wars I-VI. So, the same might go for Morgana. Anyway, it can be done.