I would recommend the surgery, providing it is being done by a board-certified orthopedic surgeon. At 5 years of age, she has only lived a third of her expected life span, and 4 months of recovery isn't that much in the grand scheme of things, compared to 10 potential years of arthritis and pain if she is not operated on.
That's just what I would do. Other people, who have had dogs that have actually gone through the surgery, will weigh in with their opinions. You may wish to have this thread moved to the
Sick & Injured / Emergencies Talk forum.