What rear reinforcement would be good for someone with osteoporosis?

A back brace will not help for the back to put it back into its normal position. If your mom needs a brace to support her back at work or if she is in pain, then she needs to go to a medical equipment store or an orthopedic doctor to get fitted for the correct one.
There are many many medications that can help with osteoporosis, which most of them only stop any further bone loss/weakening from occurring. But honestly I don’t think that there is a treatment out there, no matter what the claims are that can actually reverse the effects of osteoporosis. You need to take your mom to a physician and have her checked out. They will take into account her history and other meds that she is currently on before prescribing any thing for her. There is no one on this site that can recommend any meds without knowing her history and examining her. I wish you the best of luck, but this is something that needs to be discussed with her practitioner.