Hello,
Your mother's glucose levels are quite high and certainly need treatment. Glucovance is a well accepted medication used for Type 2 diabetes and will most likely help bring her glucose levels down.
Changing dietary habits is crucial to doing well: specific things to avoid include regular sodas, sweet drinks such as sweetened tea and juices, cakes, cookies, candies etc.
Try to keep carbohydrates(starches) more complex instead of simple, for instance wheat bread instead of white, brown rice instead of white. Vegetables that are non-starchy, such as carrots, lettuce, spinach, squash etc are very good. Keep fruits in the diet but watch for rises in blood sugars. Drink lots of water if other medical issues allow(if your mother has heart issues she may not be able to drink lots of water).I strongly suggest meeting with a diabetes educator or dietician to review your mom's food choices and do some meal planning. It is much more comprehensive than I can offer in this post.
All the best.