I´m sorry for taking so long to answer, I had to think to write this:
Well, I´m afraid I thought too much about a backstory for her so far... She is tone of three sisters, being the middle. Her older and younger sisters are fully human, but she have to always hide her face and body, because she is not entirely human..
This is only the beginning of what I thought about her... If you would like to know more, just tell me...!
No problem. Her background sounds interesting. Kinda makes me wonder what she looks like underneath the mask. Then again it would be better if no one sees what she looks like. It would keep that mysterious feeling going^^.