Thanks for your question on Health Care Magic.
I can understand your daughter's situation and problem.
Possibility of
stress and
anxiety related symptoms is more in her case because at the age of 15 years, heart diseases are not common.
But better to get done ecg and 2d echo to rule out cardiac diseases first.
If both are normal then no need to worry for heart diseases.
She is mostly having stress and anxiety.
So better to
consult psychiatrist and get done counseling sessions.
Try to identify stressor in her life and start working on its solution.
She may need anxiolytic drugs too.
Don't worry, she will be happy.
Ask her to avoid stress and tension, be relax and calm.
Hope I have solved your query.
Wishing good health to your daughter. Thanks.