I think it varies depending on the child. Also, of course, it does take time to identify signs of an approaching hypo, even for an adult. There are subtle signs which you learn as you go along.
Moreover, in some circumstances it's possible to miss or confuse the signs eg if an adult's main symptom was feeling hot and sweaty, and they were at the gym, you can imagine that any hypo would be less apparent when they're sweaty anyway, and probably feeling tired.
Has her team offered any tips? Eg talking to her about how she feels at, say, 3.2, to help her identify any signs?
The only child similar in age with Type 1 that I know tends to either get emotional and/or 'run out of batteries'.