I was someone who had parents that did not deal with emotions very well.
I was a Ballet dance from the age of 4 to 19.
I am painfully shy to some degree, it was worse in my younger years.
I was so shy that I alienated myself from my dance class for the first 4 years I was going there.
As soon as I felt ok to come out of my shell.......My group because instantly closer and we were about the best troop ever to come from my Company(have not been in ten years so this is probably not true true now).
You ave to think, they all are at that age where hormones are just starting to take part in there body. Meaning they will be more emotional. More sensitive to pain, failure and fitting in. Competition at a a young age is fair and fun. When the kids start feeling a bit more pressure pursuing their ambitions, emotions can start to play into how she processes things.
I put so much emotion into my dancing, that I never flinched on the outside the first four years I was dancing with absolutely no friends. I turned my shyness into something considerably beautiful at a very young age.
I say dont play into the whining emotional stuff that is superficial.
Reaffirm her where you can. Reassure her when she thinks she is not good enough.
She can get through these changes without being an emotional mess. She just needs to know that is what is going on. Then she can correct the misbehavior and deal with those feeling.
Maybe she needs a break from competitive sports? I would think that could do a number on ones anxiety. Remove the stress.
It is not quitting, if you are just taking a break