I don't have any guidance, but I can commiserate, especially about the injury concerns. We're dealing with something like the same thing, though your DD sounds further ahead than my DD9.
We actually managed to put the brakes on DD's enthusiasm for gymnastics when she was five or six, by describing what life looks like for Olympic gymnastics trainees. Living away from home? Little time to play? No thanks, she said.
She continued to train at a moderate pace, with targets of individual skills she wanted to acquire being the limits of her gymnastic ambitions, but somewhere along the lines she became obsessed, to the point where she was constantly tumbling at home, began coaching her friends, started watching videos online and unlocking certain skills on her own, etc. Now she's one or two steps away from the local gym's competitive team, and closing fast, thanks to an excellent work ethic, and she's pushing us for more training opportunities. DD's Christmas list is very short this year: bars, beam, and mats. She wants to turn her play room into a gymnasium.
We're doing basically what you're doing... trying to be good parents and feeding her passion, while secretly hoping she doesn't break her neck.
