Diet and supplements for a diabetes patient? and things to avoid?

I am asking this for my mom. She takes insulin and feels sick often. She's not too old, in her 40's but it feels like shes 80. She often feels pain at heart, and her legs and arms
right now i believe her diet SUCKS. she's not obese even though she eats alot of oily food, but i think it does effect her diabetes. so any tips and suggestions will help plus a complete diet plan [breakfast,lunch,snacks,dinner] and things to avoid…
thanks