1- In 2x10 she choosen to save her sister over kill Uther; because if she was "pure evil" like her haters say, she could sacrifice her sister and kill Uther (but she don't, and she could do it if she wanted because is a powerful woman, but no, she prefer to save her প্রণয় sister when Merlin "good guy" abondoned/poisoned Morgana);
2- she could be villainess, but she is loyal to persons that loves:
When Morgana was afraid without nobody to help her, who's in her side? Morgause. When Morgana was a overrated, who's respect her for herself? Morgause. And who's protect her when even Merlin and Gaius...