So I just had a rather strange set of thoughts. We know that Maggie was close to the Fey, surprisingly so. We also know that Ebeneezar is Harry's grandfather and has the blackstaff, something used by the Winter Crone. In addition Harry was told by Kincaid that they were equally human, both being Scions. A strange thought came to me about Ebeneezar seducing the winter crone back when she was the queen of Winter and perhaps taking advantage of that to steal the blackstaff. And his daughter was in fact part fey. This may be in the extremely silly angle of things but the idea popped into my mind recently and it feels stragely compelling