A couple of years ago, I had some quite bad attacks of this and spent two periods of two weeks in hospital on a heart monitor. The consultant finally diagnosed that I had had a viral infection which had attacked the heart, Myocarditis. see
http://yourtotalhealt...eart-myocarditis.html It comes out of the blue.
I would be OK for a while and then my heart would go into spasms. It took me nearly a year to recover and still have some arrythmia.
She should go back to the doctor and get it checked out further. It probably is not this and most cases recover but there is the occasional one where it can get more serious, but mine started just like hers.