SHe'll have to start doing with with the coach, with the coach giving her less and less spotting as she goes on.
For some gymnasts, even the slight touch of a hand is comforting for them even though a hand on the lower back might not actually contribute anything.
She will eventually have to go for it herself, maybe trying it on a crash mat or softer floor mat. She'll have to remember to keep her shape as with a lot of gymnasts as they go to do back handsprings by themselves for the first time, they close in their body shape, bend their arms and legs and end up flipping on their head...and then it becomes a vicious circle as they won't do it by themselves in fear of getting hurt.
Encourage her as much as you can, and so should the coach