My daughter, who is now 20, has severe spondylolysthesis and is completely done with doing gymnastics or other major sports. She had some minor issues when she was 10 and a L 9 training L 10 with a stress fracture in her L 5 that healed. It didn't flare up badly again until she was 18 and in her first year and training for D I college gymnastics. The trainers tried to do a year of PT thinking it was just the stress fracture flaring up but when she finally came home and I brought her to an orthopedic specialist, he said she had very high grade level 3 spondylolysthesis, pretty much a 70% slip of her vertebrae. I, of course, went mental. He had her in a higher grade back brace (oh did little miss fashion HATE that! lol). This past summer she finally had a pretty extensive surgery that involved fusing some of her vertebrae, all the way to her L 4, and relieving pressure off her spinal cord. She's still recovering, even though she went back to college (away from me to take care of her, not thrilled about that!), although to a different school than where she did gymnastics.
I hope you and your DD don't have to go through this! My DD is pretty heartbroken she can't do gymnastics anymore, although I think she's done a great job dealing with it. Sitting there while your child is in surgery is not something I would wish on my greatest enemy. Godspeed and good luck!