There are a some things that can be done for Molly to reduce her pain and help her feel better!!

You have to work with the affected legs. Stretching them is an excellent way to battle arthritis. Pick up the sore legs and stretch them slowly forward and backwards, about 10 times. Do that exercise about 3 to 4 times a week. By doing this it helps the cartilage in the knees, and helps the soft tissues. The stretching also works the muscles, improves the circulation to the arthritic areas, helps prevent injury, etc.

Hmm...what else might help Molly!?!? *Thinking*

Call the equine vet and talk to him/her about possibly putting Molly on joint supplements. There are many nutrients that help the horses joints, and the supplements that the vet gives you will improve the joint health of Molly. This is probably the most important thing.

Put ice on the joints. Hold it on there for 5 minutes then take it off for about 15 minutes, then put it back on for 5 minutes. Do this about 3 times in a row.

You could also put on a standing bandage to reduce the inflammation/swelling of Molly's joints.

EDITED TO ADD: 22 years old is not too terribly old, she can still be treated. There are horses at my local barn & camp that are 30+. Heck, old man Thunder passed away a couple of months ago at the age of 36 I believe.