I mean they don't have to actually live as girls. Realistically, most of them, when genderbent, wouldn't actually alter their gender that much. When that happens, what they could do to feel more comfortable is to change their gender presentation back. This would be done by cutting hair, keeping clothes, wearing binders, or other things transmasc people do. There's no way that the "most powerful" witch couldn't conjure up the things they all need. Best case scenario, she's able to make some testosterone. The people who are "level 1" should also be able to quit attempting to be witches.
Anyway I know none of this would actually be written, as seen by the first chapter, but a girl can dream, right?