I'm really sorry to hear that Amy is in pain, I know you have always worried about her when the weather changes. I worry that my Miss Zoomalot hurts because of the number of times she will slam into a wall as she races around and something startles her.

You can get Cosequin very easily which is made for horses, dogs and cats. I have some from the shelter for my elderly fosters.

You might want to try TTouch which is a type of animal massage, mainly for stress management and the like but also used for arthritis. I heard about it through Best Friends. This site gives you information about t-touch books so you can learn to do it yourself:
http://www.ttouch.com/productsBooks.shtml