Diabetes can be a highly individual thing to manage. I assume your Mom has a blood glucose monitor kit where she can measure her blood sugar levels. Keep in mind that corn and peas are starches. They convert to sugar through digestion. This doesn't mean your Mom can't have corn or peas, but she should take it easy depending on how many carbohydrates she has at a meal.
Bananas are also high in sugar.
A basic rule of thumb is that if a diabetic wants to eat a banana, eat half a banana instead of the entire banana. Protein helps slow down digestion. She or you should visit the web site of The American Diabetes Assn. The ADA can be of great help in meal planning. Please keep messages on topic.