93 yr old mother has osteoporosis now four fractures in her pelvis... Spontaneous? . Does she do rehab but continue to have spontaneous fx or does she become bed/chair ridden but pain free?

Forteo. If there has been difficulty in healing of one or more of the fractures it is possible that treatment with Forteo could produce healing. This is the only medication that stimulates new bone formation.
Try Rehab. It's tough, but also depends on how quickly the fractures occurred relative to each other. If it was over a while, then another rehab shot is worth it. If they were all close together, then considering her comfort and a palliative care approach is a good idea as well.
Stress fractures. Of the pelvis are common in osteoporotic older women and underdiagnosed. In my experiecne either a bone scan ct scan or MRI has picked these up. They should help with proper physical therapy and treatment but please consult your doctors. They usually also add a biphosphonate or some medication to try to strengthen the bones as well. But this can take months to heal.