I'm so sorry to hear that your Mom is having such problems with her insurance. I don't know anything about Medicare and the need for a supplemental insurance coverage. Does Medicare on its own not cover suboxone for addiction? The healthcare/insurance system is such a mess, in my opinion. I do not understand why an insurance company would choose not to cover suboxone when the likely outcome will be patients with far more severe medical problems resulting from opiate abuse. I am fortunate enough to belong to a large HMO (Kaiser) which places a lot of emphasis on preventing chronic disease from progressing. I have been in their addiction recovery programs in several locations in Northern California and their focus is on addiction as a chronic disease that is progressive and deadly if not treated. Their buprenorphine maintenance program is awesome and I really don't understand why more medical organizations don't embrace their model. Anyway, if Kaiser is an option in your area I would definitely look into it and see what the evidence of coverage for available Medicare plans covers as far as chemical dependency treatment.
The other thought I had is to ask your Mom's doctor if he or she would consider prescribing Subutex rather than Suboxone if this issue continues. The out of pocket cost of *generic* Subutex is generally far less than Suboxone. It's definitely worth inquiring about if you have not already done so.
Again, I am so sorry to hear about the problems you are having and I hope everything works out soon.