My sister just had an ultrasound and found no heart beat (she was 10 weeks). she has a flight in two days, is there any reason she shouldn't fly?

Miscarriage: If the fetus of a pregnant woman has no heartbeat, there is no way to tell, when the pregnancy will be aborted. An abortion is heralded by uterine cramps and spotting/bleeding, eventually the passage of the "products of conception", i.e., tissue clots. The quickest way to end this situation is by performing a dilatation and curettage, i.e, surgically emptying the uterus.