Can Stage 3 Diabetes In An Elderly Person Be Controlled Through Diet?

My mother is 83 year of age. She has been a widow since 2013. She had a recent visit with a Nurse Practitioner in Texas. I have not seen the results, but my brother has. Based on what he is saying is that her sugar level is 300, apparently stage 3 diabetic. There could be concerns with kidneys failure, not sure. She has been drinking and eating way to much sugar laden liquids and food. The advise given is to do away with all sodas with sugar, diet is okay and 1 beer a day. Plus, foods that are with sugar. Plus, she has not been taking her prescribed medicine. She is now following the advise from the Nurse Practitioner by eating the right foods and drinking water, a diet soda and beer a day. My question is whether this approach will control her glucose level? Should she also be using a Blood Glucose Monitor? Is there a monitor that is used on the wrist and not having to prick her finger for blood? I hope to speak with the Nurse Practitioner on Monday to get her perspective vs. my brother s understanding of the circumstance. At what point should she be seeing a specialist vs seeing a Nurse Practitioner. The Nurse Practitioner is located in a Medical Clinic with Physicians.