I can think of a few things.  You haven't said much about your sisters but from what I gather you don't like them at all.  Explain why a bit more and Myir might be able to get something.  I have a feeling it's got something to do with her sisters or something related to them is my guess as far as her dark half goes.  That's just my opinion goes lol.  At least you can use her sisters as another way to get at her.