From my own experience ectopics can be caused by over-exercise the day before an ECG. So if she is keeping up a high level fitness regime with much exercise, I would advise her to rest up for three or four days before an ECG.
If it is from a normal lifestyle, then the only way to find out is to go to Gatwick and get their opinion. It may not be medically correct, but it is the one you will have to live by if you choose aviation.