Exercise Ideas for a Disabled Dog?

I have a 3 year old Chihuahua who was born with left paw bent inward (like an elbow bent). It is not painful and she uses it like a human uses it, as a crutch. I worry that she doesn't get enough exercise and she is overweight. Any suggestions on what type of exercise I could give her? Walking on three paws can be rough and she can do spurts, but can't really walk far. We play with a latex ball which she enjoys, but she gets tired quickly.

By Arlene J from Marion, IL