There is a joke about the difficulty of armchair quarterbacking this one, but I will resist the temptation.
My best guesses are that she could be undertreating the hairs, or she could be getting breakage from the thermolysis bursts. In either case, you could have hair coming out of a scab in two weeks. The only other option that I can think of off the top of my head would be one where you have those “double follicles” where two hairs are so close together that they look like two hairs coming out of one follicle. You may notice many of these on your legs, especially around your angles and where ever your socks grip your leg.
Working that area is always a game of competing purposes. You don’t want to hurt the client, but you want to remove the hair. The treatment modality used can give its own special problems, and getting a good insertion is no small affair as well.