Of course. Chiropractors are good for any neuromusculoskeletal (nerve, muscle, bone and joint) problems. Especially joint issues where it tends to degenerate with time due to fixations/adhesions, you shouldn't delay in getting your problem looked-at.

Would be best to wait a bit till she's feeling much better from the surgery. When she can walk, that would be a good indication that she's ready for chiropractic. Did she undergo operation for both knees?