That is an excellent question and one that is very important that she discuss with her primary care doctor
or the physician taking care of her while she is pregnant (her OB/GYN). The history you have provided is concerning for her possibly having an allergy to bananas and one of the questions to consider is if she has ever had an issue related to bananas before. If this progressed further, of course it would be important to call 911 or have her urgently evaluated for allergic reaction but if this improved on its own, which it hopefully did, it is still important that she discuss this with her doctor as she may have an allergy and they need to do some tests on her to decide if this is the case. They may also give her an injection that she can administer to herself if she develops an allergy again in the meanwhile. Regardless, until she is evaluated by a doctor it is very important that she not try to eat bananas again as the next time she may have an even worse reaction to the banana then she did the first time. If this happens again, please call 911 or get emergency care as soon as possible.