Some doctors are using a device that emits pulsed electromagnetic field (PEMF) in cases like this. A recent study in The American Journal of Orthopedics reports good success with PEMF. One hundred patients with failed fusion used PEMF for at least two hours every day for 90 days or more.
Two-thirds had a good fusion with this treatment. It's inexpensive and avoids the dangers of another operation for patients in poor health. Ask your doctor about the possibility of using PEMF with your mother.