My guess is she's a were something. In the books there are werewolves, werepanthers, etc. So maybe a weretaur? In the preview for next week she says "i know what you are" to Sam, so who knows, maybe she's just an advanced shifter or yes, as Rich mentions, probably just an acquaintance of Mary Ann.
I must say, I am disliking the whole Mary Ann angle very much.