Why are you switching back to meloxicam? Was the Previcox not working? There are quite a few new non-steroidal antiinflammatory drugs (NSAIDs) available for dogs. Some work better than others in individual dogs. All are reasonably safe.
If your dog got more exercise in the last day or two, she might have more pain than previously. Another cause of increased pain would be slipping on floors (wood and tile floors can be very slippery) or jumping off something and landing poorly. These might respond to a day or so of rest.
Walking on the top of the paw can be a response to pain. I'm assuming that the cruciate repair was not done recently considering her age. Correct me if I am wrong. She may not have time to place her foot correctly before weighting it. Alternatively, it can indicate neurologic damage.
Pain meds, a soft warm sleeping area and assistance getting out to bathroom areas should help her through the weekend. A towel under her belly can give assistance if she is having trouble getting in and out. Stairs should be avoided if at all possible.
If she has not improved by the beginning of the work week, a visit to the vet is indicated.
Let me know if you have follow up questions.
I'm guessing that you have tried putting the pills in good tasting food (liverwurst, chicken, etc.) and she still won't eat them.
The kidney failure may be compounding the problem. It makes them feel lousy and have a poor appetite. Low protein diets (Hill's K/D, spaghetti and butter or tomato sauce, etc.) reduce the protein metabolic byproducts that decrease appetite, antiulcer meds (ranitidine) and fluid therapy can prolong decent quality life.
At some point the geriatric problems increase and build on each other affecting the quality of life.