Really do think it’s clear that there are many faulty sensors around at the moment. 5 of my last 7 have failed either at the start or half way through the two weeks ultimately giving false results just before failure - just as you said. I have advised Abbott and got some replaced. Difficult to comment on your daughter, does she have a history of being low at night and rely on the Libre alarm. Perhaps have some extra carb before bed for tonight.