How about your mom, or you as her representative, ask the doctor what specific criteria will be used for interpretation of the test and what the threshold for treatment recommendations will be used. Then, where is the data to support that approach other than the doctor saying "I always do it that way". Is there data showing the benefit outweighs the risk for this specific patient? How does mom feel about taking medications, is she generally in good shape or is she very much nearing her life's end and not interested in more meds and more doctors? In the published guidelines, there is not any age cutoff for therapy although the most commonly used guideline does comment on the paucity of data showing reduction of fractures by using the suggested medications.
http://nof.org/files/nof/public/cont...upload/919.pdf
Long term studies are ongoing (google SCOOP)
and some short term studies do suggest benefit (see Medscape below)
Treatment of the "oldest old" is strongly encouraged by some authorities
Management of osteoporosis of the oldest old. - PubMed - NCBI
http://www.medscape.com/viewarticle/744882