Just thought of something.....a change of direction. Get her interested in driving. She can help with buying the harness and a cart. Horses take to driving (pulling) like ducks to water. In order to use your horse she has to provide full care when she's out, everything you would be doing, feeding, stall mucking, bedding, picking hooves, etc. The exercise will help tone her muscles. Of course she will have to walk behind the horse to teach him the preliminaries before he's hooked up to the cart.