The backstory isn't bad, I like it. The issue here is that realistically speaking, there is no way to hide such a mutation, and it doesn't come with a power as far as I can tell. You need to be able to hide your abilities without attracting suspicion. I can't elaborate more at the moment but it will be very obvious why once we are a little into the RP.
Yeah, I edited it a moment later, but the idea is that no flesh and organs means that she'd be pretty invulnerable to most kinds of damage. Bone is a lot harder to break than skin, after all. Hmm, for something along a similar line (cause I'm mean and want to make a pretty person ugly!), how about the growth of invulnerable scales on the skin?