My Daughter Is 17 And Has A Congenital Heart Disease.

My daughter is 17 and has a congenital heart disease. She has had 3 open heart procedures and a stent put in 4 years ago. Currently she has no restriction and the only medication she currently takes is an over the counter aspirin, small mg. Up until yesterday she has not had any issues. Then, during her marching band/Colorguard practice, that runs from 8am-5pm with an hour lunch, she had a short period of chest pains at 4:15pm with no other symptoms. She said that she was doing quite a bit of running at the time so her coach had her stopped for the day. I picker up @ 4:30 and aside from being a bit scared, she said she felt fine. She went back to the band camp today and is applying herself 100%. My concern is that on her lunch she told me that she's having more of the pains over her left breast. Quite a few that are 5 minutes, and she had 1 this morning that lasted almost 15 minutes. Could this possibly be a muscle strain that has nothing to do with the heart? I ask this because she just joined the Rifle line (1st time) and was thinking she could possibly be using different muscles compared to the ones she uses with her flag pole. I'm trying not to panic and run to the ER but I know that this isn't something to mess around with either.