Thanks for sharing your concern.
As she is fine now , there is no need to go to ER.
You can see your GP on non urgent basis.
If the episode of fast & thumping beats recurs & lasts over 5 minute or so ,heart beats are so fast that they are difficult to count , or if associated with breathing difficulty, then definitely ER visit is warranted.
Episodes of fast beats can be due to excitement ,anxiety
She will need an EKG (heart tracing) also to look for any rhythm disorder of heart muscles.
Hope you find the explaination useful.