All of the above comments are great recommendations. You definitely want to work with her physician and physical therapist in this matter. Continue to be of assistance to your client through the recommendations of her physical therapist/physician and keep encouraging her to do the recommended exercises.
Another great option is to recommend her to someone who is certified in water therapy. Water exercises have beneficial properties. For example, water exercises use bouancy. The bouancy properties of water allow the joint better range of motion as well as stretching the tighter muscles and strengthening the weaker muscles around the joint.
I hope this information is beneficial to you & your client.