My dd has scoliosis. A 24 degree curve (now) that required a brace at night for 15 months. When she was diagnosed and had a rapid degree change we immediately stopped all walk-overs of any kind. And all bridging. I think it helped stopped the rapid change. My younger dd, when she was diagnosed, we stopped walk-overs and bridges as well, as a preventative. Hers has never gotten that bad, I think only a 15 now. Our doctor agrees that gymnastics is good for them. However equated the walk-overs and bridging to hammering a bent nail. It will bend more with repeated hammering. That is why we stopped them. I feel that it worked.
I am surprised that your dr thinks she has 3 more years left of growth when she has already started her period. Usually girls only have about a year left. But everyone is different. My dd is supposedly done growing (according to her x-rays) however she has yet to start her period.