Mother is 77-years young (as she likes to say) and very active. She tore her rotator cuff playing tennis and had surgery to repair it. Unfortunately, it's been six months and she still has not regained her motion. Her shoulder pain seems worse than before the operation. Is this typical in someone her age?
It may be difficult to answer your question directly without knowing more about the shoulder injury and type of surgery done. In general, older adults have degenerative changes in the joint and soft tissues around the joint. Rotator cuff tears (RCTs) are common.

There can be tears in the joint cartilage or just frayed edges that need smoothing down. Sometimes repairing the torn rotator cuff is all that's needed. If the torn cartilage isn't bothering the patient, then it's not always in their best interest to repair it. The result can be the loss of motion and worsening of symptoms you described.

In other cases, the rehab program after surgery is the key factor. The patient must follow the surgeon's and the physical therapist's directions carefully. Too much movement too soon can cause the repair to fail. With the right program, loss of shoulder motion can be avoided.

It might be best to make a follow-up appointment with the surgeon and go with your mother. Her age may be a factor; sometimes older adults just need more time to progress through the rehab program. She may need an extra step in the rehab process.