I would stop the pain pills immediately. They are not necessary for the healing. How is her incision looking?
Not all cats can tolerate it and it can be hard on the kidneys and liver and this is a sign that she is not tolerating it well.
From this website:
Gastro-intestinal, renal and hepatic function should be monitored periodically in animals on a long-term therapy. Treated animals should be monitored for the occurrence of side effects. Adverse reactions considered typical of NSAIDs include gastro-intestinal ulceration, renal toxicity and hematological abnormalities. NSAIDs present a greater risk in animals under 6 weeks of age or in aged, debilitated or sick animals. Tolfedine should be used with caution in these cases; careful clinical monitoring is advised. In the event of gastro-intestinal signs (e.g. loss of appetite, vomiting, diarrhea or melena), or adverse drug reactions (e.g. lethargy, behavioral changes, abnormal bleeding), treatment should be discontinued.