She looks like the body type that doesnt build muscle easily. Usually at the beginning, they can keep up with their peers but as the difficulty level increases they struggle. It was always explained to me that if a gymnast looks slow and sluggish, it is because the muscle ratio is too low. Which is why it is often the case after injury or extended time off. The gymnasts who are able to comeback with relative ease is because they naturally retain muscle or have been able to maintain their fitness levels through other physical activity.
I mean, this could all be nonsense, some of my colleagues believe some weird things. But it does make sense.