Please. Today. Find a different Cardiologist. It could very well be only a matter of time before a heart rate like that churns up a clot. As a School Nurse- I would have a hard time allowing a student with these symptoms to participate. Was she cleared during the time that she was having this many symptoms?
This sounds very scary. Maybe even ask for a Loop Recorder to be implanted to monitor continuously.
I'm sure you've been asked this a gzillion times- but seriously, does she consume very much caffeine? I am the biggest critic of Energy Drinks in all ages. But, I have the loudest voice to teach kids/adolescents about the dangers of them.
Many blessings and hopefully you can find the right Cardiologist to help get to the bottom of what is going on.