My motheringlaw has bad painful arthitis in her shoulder and arm is dietbetic what do we do to heal her?

No healing. Rather there are excellent treatments out there. She really whould see a rheumatologist for her arthritis (rheumatoid versus osteo) and an endocrinologist to get her diabetes under control. Diabetes can exacerbate arthritis. Gentle water aerobics are also a great way to help, plus she could make friends in the water class.
Many options. See a board certified Orthopedic doc- many options which depend on overall control of diabetes and the conniptions that need to be treated.