She’s more than strong enough in the gym to do anything on the track. Seems like she should ration her energy a bit better, not so much bias toward the gym. But I suppose that depends on her goals. Does she want to be a successful sprinter? If yes, then she needs to expend the majority of her energy running the sprints. The weights are a supplement, not a substitute for track training.
It’s so hard to be prescritpive without seeing the athlete move. Maybe it’s a biomechanics issue. Maybe she’s too tight around the hips to keep it going over 200m, but I agree her 100m is much better than her 200m.
Maybe just try to design something for her that encourages her to relax in the longer reps. Perhaps some splits runs may suit, give her plenty of recovery time early. She sounds like a pure power creature… wish I could offer more.