Okay, Medusa would be an adorable fit, and I like the powers you have in mind for her, and I wouldn't mind helping you expand on those if you're set on it. And also had some other (very horrible) essences in mind, like the Little Match Girl, Eurydice, Baldur, Achilles, or Cú Chulainn, but then I looked over her description, and I thought of something perfect.

Snow White. Striking white features, rotten luck and tormented by the people she lived with until finding a new home, keeping a tight hold of her kindness, happily doing their housework, killed by a family member (even if the motives are vastly different), dying young but her grave plays an important role in her story? I think Snow White would be an amazing match, and we could come up with some great powers to go with it too.