Nightshade is the 11-year-old daughter of an assassin. She is anti-social, clever, always dressed in black, has short black hair, and always uses nightshade in all her potions.
I'm not a Skyrim expert, so this won't be perfect. I've gotten Lucan's golden claw back for him, killed Grelod the Kind, and killed Astrid. I've been a few other places and watched my daddy play a little bit. That's it.