Could this be a Negligence case?

My sister has had neuropathy in her feet from unstable diabetes for a year now. It has progressed every month, to the point she can barely walk. :( Her last diabetes doctor essentially said 'You know what diabetes can do.' and that was It. For years she didn't find a plan /way to help assist to lower my sister's sugars- they are very insulin sensitive, so she could barely ever take much insulin. Her sugars unfortunately therefore, remained high, year after year. And last year before her last appt. with her, she said' I don't know' (about how to treat sugars and also neuropathy) and basically then hung up on her. As a specialist,would one not try to Find out then? Any answer or any plan? My sister feels her brushing her off was negligence and she did get worse , from not being treated.

This also occurred with a nerve specialist, who only mentioned a vitamin she could take for neuropathy , then just advised my sister talk to Her PCP for a med for nerve pain. She felt yet Again pushed off- there were multiple treatments out there for neuropathy, and she was not informed of any. And now it is worse , and could be permanent. What are your thoughts? She is at her wit's end, getting no help and having to research treatment on her own.