I don't think it was mentioned anywhere the healer lady herself wouldn't get tired. It was just said the patient themselves wouldn't necessarily have what it takes. So, there's no proof as of yet the lady could go around healing a hundred people as long as the people being healed didn't run out of stamina. However, looking at that cold/hot dude, I don't think personal energy is of much issue in this show's world when using the super powers. Freezing and thawing that whole building so fast should have taken quite a staggering amount of energy. Obviously more than a fit looking person would have in his adipose tissue.