Hormones are more important to fat gain/muscle gain than you think. You cut for a long period of time without refeeds, your hunger levels go through the roof due to lower leptin levels and higher cortisol. Like up to 100% higher than average. That is why hormone management is so important, and not being overzealous in your training.
What I actually suspect happened is that she trained too hard, which happens often with bodybuilders.