How about "Foster Child of the Winter Court" ?
That would, for me at least, sum up pretty well what you said about her so far.
Origin unknown, growing up without really belonging, being ignored, sidelined, being raised as something you aren't.
Invoke for: knowledge about Winter, maybe some contacts, but also when going against Winter because she never really belonged. Social stuff, because you do have ties, even if they are brittle.
Compel to:
Make her fail socially in a Winter Context, make her be resentful against Winter, make her want to help a lost child...
I'm sure with the sneaky backstory you have on hand you'll be able to think of many more possibilities for Invokes as well as Compels.