First determine if the issues are front or rear leg mobility, if support is short term or rest of life. When your dog appears to be in a lot of pain when walking, it's time to consider a wheelchair. Dogs must be taught to use the equipment. Test your dog's reaction to a wheelchair by lifting rear or front end with a towel to see how she manages. Watch your dog's reaction after several tries with the towel over a period of several days. Even dogs that have mobility problems benefit from a bit of exercise and being outdoors and a wheelchair can provide that. Have you tried giving your dog glucosamine/chondroitin with MSM? It has shown to be helpful for arthritic dogs.