My dog chews her back constantly. I have tried everything, and the only solution by the vet is to put her on steroids! Any advice?

If you've tried everything else and nothing's worked, then steroids are probably a good idea. I've had dogs who needed to take them for this and they worked really well. Be prepared, though: Some steroids may make your dog very thirsty (so more trips outside) and they may cause some stomach upset, particularly early-on (which also means more trips outside). Be sure that the vet regularly does bloodwork to check kidney and liver function.

Akoue, had to spread the rep but I agree. Steroids may be the way to go. :)

With steroids the thyroid should be regularly checked as well.
My parents had a dog that was also prescribed steroids for the same thing - they finally listened to me and started feeding him Canidae Lamb & Rice and no longer needed to take steroids. (A personal experience that might be helpful.)
You said you've tried everything... Switching food brands (Canidae is excellent, especially lamb & rice); washing materials (such as the dog's bed, etc.) it comes into contact with, with a hypo-allergenic, dye and scent-free detergent...
I wish you and your dog the best of luck and good health.