Most orthopedic surgeons will be able to tell if there's laxity in the knee, with just a light sedation of the dog. I would probably put your pup on rest, and just see the specialist if she doesn't improve.
Really no need for your vet to x-ray again, as there's a high chance the Specialists will also x-ray. My daughter's dog has had three different surgeries on each knee. They are painful, and require strict rest. It's going to be a tough couple of months, if she does require surgery.
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