The problem isn't always over training with these young high school girls, it's never having down time in a year. They train and lift like pro's but they race a schedule of hs athletes. They start racing - even if tempos - early september. Nike is early december. Indoor is already in full swing so they jump in some shorter events, or like touhy - run hard 5K. Then it's milrose, then states, nationals - mid march. Outdoor starts Early april, even if you skip a meet or two you are full racing last week in april. Nationals is mid June. So maybe two weeks off in June - July and August become the only down time the whole year. Pre-season in NY starts August 10th or so. So maybe 5 weeks - but from what we see with hs kids is the work really hard in the summer. As the body matures it needs more down time, and more recovery. If you don't give it, the body will get injured.
That being said, I believe she trains very hard and a lot. Her interviews say workouts are crazy hard. She clearly lifts a ton. The meets I've seen her at - she does 10 miles or so on race day. So it could be a combination of the over training, and minimial down time that catches up with these young kids.