getting her weight down should help enormously with her hind leg/back problems.
I put together a webpage on diet and nutrition when my 10 mth. old adopted beagle was 38 lbs. He's now a healthy 7 yr. old who has weighed a consistent 28-30 lbs. since.
<a href="http://www.geocities.com/carlyc.geo/nutrition.html">Diet & Nutrition</a>
You have to be diligent and consistent and do it slowly and the rewards will come to both your dog and her health.