I imagine she's hearing this correction during dance movements when she elevates her arms, and on skills where her arms should be in a straight line that starts at her hips and ends at her hands. That covers a lot of gymnastics, so she's in poor posture in her handstand, cartwheel, walkovers, back handspring, and round-off......and that just the beginning.
The rib problems are caused by one or more of these conditions.
Body type
Resting posture where she pulls her shoulder blades back and slightly together.
Miss-understanding..........
which muscles are used to raise and keep her arms over her head, and not knowing which muscles should be used to support her weight when in handstand type skills. Eventually she'll learn what she needs to do to correct this, and I hope her coaches keep up the reminders, and maybe provide her with an occasional refresher on when and when not to use the muscles that pull her shoulder blades together.