Don’t let her hold backbends. Especially if she has non flexible hip flexors or shoulders, it puts a lot of strain on the lumbar spine and can result in some very serious problems later on.
She is 6 so she is in the peak window for developing flexibility, kids window of opportunity to best develop flexibility is between 5-8 years of age. After age 8 kids can still develop flexibility, but it is much harder. Since she is not naturally flexible, it is important for her to take advantage of this developmental window, because it will be even harder for her later on.
I would definelty discuss with the coach, what areas she should be focusing on for stretching at home, naturally flexible kids can develop it enough with the stretching done in class, but naturally tight kids need more.
Tips for stretching at home include
1. Warm up properly first. Have her do jumping jacks, jump on the trampoline, skip with a skipping rope for a few minutes before doing any stretching to increase the blood flow to the muscles.
2. The go into some general and light stretches, like arm circles etc to increase the mobility of the joints before doing big stretches like splits and bridges.
3. Then do the stretches recommended by the coach, holding the, for the length of time recommended by the coach.
4. Don’t allow her to bounce in any stretch, and don’t push her into any stretch, just leg gravity do the work.
5. If she is doing bridges, have her do them with her feet on a surface raised at least 30cms, this will take the stretch out of her lumbar spine into her shoulders.