I'm guessing you mean to use a trombe to leech her excess power off and at the same time get lots of quality material for paper making. Seems like a pretty good solution, but I was thinking there'd be a possibly easier and more useful solution, of her just learning magic and just using the mana that way. The magic tools have to come from somewhere and if there's magic tools, then I feel like magic should exist too.
Yeah, there's definitely multiple solutions, but this was one that seemed to be readily accessible to her as a child. Hell she stumbled upon one and at least two more popped up in the story offscreen, and it didn't seem like it was the boys' first time dealing with trombe. I'm also fairly sure that despite her VERY short exposure, she was "cured" of the symptoms of the purge for quite a while.
She can't learn magic/create tools yet because she has no social standing or basis to be dealing with magic yet. Now that the events of episode 14 have occured and she's under the protection of a generous benefactor (the head priest), it may become a possibility pretty soon. All in all, she just needs to bide time and make it to adulthood at this point.