Can you recreate and palpate any posterior structure that is painful?

Was their any erosion to the underside of the patella or the articular surface on the femur. When in range is her anterior pain? Does unloading the tendon with strapping tape reduce the pain? i.e. can you definitely say the pain is from the patella tendon.

Furthermore is the pain the same now as it was pre-op or is this a new pain? She might be back to the original pain. Check for neural tightness/restriction in the area and at the proximal tib/fib joint.

mild to moderate patella tendonitis
This was probably there pre op as well so might not be worth much. In terms of eccentric work - this is generally good for an tendinosis e.g. of the Achilles. It might only be aggravating things here as the patella tendon might already be failing. Get the client to work more and think more about the ankles and hips, glutes, soleus and hamstrings. Then focus less on the knee itself as it is just a small hinge that in general moves when the other joints more to keep the center of gravity balanced. I always think of it as a door hinge. If someone swings on the door repeatedly the hinge fails. But there was not problem with the hinge. Get what I mean?