there are many causes of rapid heart beat..
most common of them by far is anxiety and mental stress.
some heart beat problems also cause such problem which we call "supraventricular tachycardia".
But until and unless we have an ECG that shows supraventricular tachycardia we can never label a person to have heart disease.
Next Steps
1.most important next step is to relieve anxiety and mental stress if at all.
2. Try to get an ECG recorded during an episode when she has rapid heart beat.. IF ECG during that time is normal then she does not have any heart disease for sure.
3. get
thyroid test done..
TSH, T3,T4
4. if problem still persist get a 2DECHO and 24 hour HOLTER test done.