Diabetes can be controlled, it cannot be cured. Your mother will definitely have to modify her eating habits to make sure that her blood sugar, blood pressure and heart problems are under control. Please realize that if diabetes is not in control, i.e. if her blood sugars are very high consistently then it can directly affect her heart, kidneys, eyes and nerves. Hence, it is very important that she brings her diabetes under control.

Good nutrition for older adults is often a real challenge due to limited incomes and living conditions.  Many older adults living alone do not take the time to shop or prepare meals...and eating properly takes planning.  That being said, diabetes can be managed through diet and exercise.  An excellent book on this subject is Dr. Bernstein's The Diabetes Solution.

In short, the best food choices for diabetics are the foods which either contain less sugar or convert to sugar more slowly in the body.  Sometimes these are referred to as "lower glycemic index" foods such as asparagus, spinach, green beans, etc.  You may look on the internet to find lists of the glycemic indices for the majority of foods.  Often you can pair a higher glycemic index food (such as an apple) with a higher fat food (like nut butters) and slow the release of insulin in the body.   Also, getting a sufficient amount of protein and pure/filtered water will be important for your mother. I support the use of stevia, in lieu of any artificial sweeteners. 

You may wish to consult a health care practitioner to assist you in developing a more detailed nutrition plan for your mother's conditions.