Treatment options for arthritis in cats are more limited than for dogs, unfortunately, but they basically fall into two categories: drugs and supplements (most of which are available at local pet/grain stores or can be purchased online).
Supplements which may take a delayed time of several weeks to be effective
1 Cosequin for Cats which is a joint supplement that contains glucosamine.
2. Fish oil supplements such as Welactin which is liquid that can be drizzled on the food. Fish oil can help to reduce inflammation.
3. Adequan which inhibits enzymes that break down cartilage, so joint damage is reduced; it's an injection and needs to be given by your vet.
4. NuCat Senior which is a source of antioxidants to reduce oxidative damage to joints
Drugs which tend to work fairly quickly.
1. Occasional use of anti-inflammatory drugs such as Onisor which is licensed for use in cats but can only be given for three days in a row.
There is a drug called Metacam but it is somewha tcontroversial in veterinary medicine, at least here in the States. It's use has been associated with significant damage to the kidneys and should be used with great caution in older cats; the drug currently carries a label to that effect. However, there are some recent studies which indicate that at very low doses, this drug maybe beneficial for cat with osteoarthritis.
2. Pain medication such as Buprenex can be very useful and could be given every day or only on the days that she needs it.
Alternative therapies such as hydrotherapy, laser, massage,acupuncture/chiropractic adjustments may be of benefit although these therapies are often better suited for dogs than cats.
I hope this helps to provide options for you to consider. Deb