I don't have personal experience of this in cats either however our dalmatian 3.5 yr old boy has it & we give him Synoquin which is basically glucosamine & has made a difference not sure of dosage for a cat though, Banjo had 6 weeks of 1500mg a day & now 500mg a day

He also has a bioflow collar (magnetic) which is very good you might be able to get one for your cat.

Banjo also has metacam but we are worried that might do more harm than good longterm he has to have a blood test each year to check he is ok with it.

Good luck & I hope she picks up soon x