And don’t look past ROM work as very likely being sufficient stimulus right now. I would have this client stand with support (hands on a wall or rail) on one leg and move the other leg through hip ab/adduction, hip flexion/extension, knee flexion/extension, ankle inversion/eversion dorsa/planarflexion. And shoulder ant/post/lateral arm raises to shoulder height or tolerance if there is discomfort on the way up/down. Elbow flexion/extension. Wrist flex/extension both laterally and post/anteriorly. When most movements are doing well and the client isn’t experiencing post workout issues, add light tubing or have the client gently tense muscles during the movements. Progress from there, heavier tubing or more muscle tensing. Eventually you may be ok to add a load like dumbbells or a cable machine. I would also really encourage the water exercise. At that age, water exercise can be phenomenal.