I have the same issue, and I don't think there's a way around it. Currently Auntie will only give the power if you don't intimidate and you just take the deal and let her take Mayrina. I've tried this a dozen times now, all with different combinations of convo options, and she'll only give you her hair of power if you let her take Mayrina. I think the fact that the quest isn't finished after the cutscene and it won't finish until you talk with Mayrina is what's causing the issue, as the power Auntie gives is a quest reward, and the quest ends later if you also save Mayrina.
This would be such a simple fix for them, frankly I'm baffled they haven't already fixed it, all they need to do is make the hair also a quest reward for this way completing of the quest
