If you are going to have Hermione be controlled by something/someone, why not make Ron an unwilling, unknowing dupe this time? It would make for a nice change of pace from the way you've portrayed him in your other stories and since you have already written Harry as accepting of his choice of family over friendship, it would play well in having them be friends later on again. Make The Broomstick or Mummy Dearest be the controller(s), with an assist from Dumb and Dumbler. I don't really have a preference which way you take that arc, it will still be a good read regardless.