Terry and Lily (is that her name?), welcome. Your future posts won't need approval so post away. How pawesome that your girl has been cancer free and done so well for this long! 

Panting is definitely a pain indicator pets give when they hurt. It sounds like the pain is not under control and that's the first place you want to start. Did your vet do any diagnostic work before prescribing the prednisone? If so, what was it? And what was your vet's plan for figuring out the cause after starting the pred? I'm hoping they told you that pred can help pets feel better but it does not address the source of the problem, it merely masks the symptoms. It's best to work toward finding a cause so she can come off the pred as soon as possible.

Carts or harnesses will not address the source of the pain. Don't try using a cart yet, unless you are working with a canine rehab therapist who can ensure that she really does need one. This article about Tripawds and wheelchairs tells more..

Your girl has been on three legs a long time. No doubt the stress of being a Tripawd has caught up. But the good news is that usually these problems can be addressed with rehab therapy. The best place to begin is by seeing a veterinarian who has experience in pain management , as well as seeing a canine rehab therapist. Sometimes you get lucky and you find one who has experience in both areas. If your vet or chiropractor are not certified in this area, I would find one who is. A good pain management vet and canine rehab therapist will address the cause instead of just masking the symptoms. 

If you want to share where you are located I can search for a rehab therapist for you or you can click on the "first rehab visit " link and read how to find one. The best part is that the Tripawds Foundation will pay for your first rehab visit !