@Jaegrqualm
From what I gather what put her in immediate danger was her constantly switching from kid to adult and vice versa so as long as they avoid that she shouldn't be in peril of conking out on the spot.
Staying in kid form kills her slowly, she was in that form for over a week before she started breaking down, so as long as they don't have her stay in it for too long, which seems that way since they just want her to infiltrate the school and get the oddity, she should be good.
@LordTrollbias I was thinking it was something that "now she does it on her own, instead of by the books power", but your reminder about how long she lasted to begin with makes more sense. (Plus the revelation that she can still do it, even without the book.)