I took a diabetes management class in 2007, when I was diagnosed (I was 57 at the time). The class teaches that you can have 45 grams of carbs per meal, or three 15 gram "servings". Starchy vegetables and fruits should be carefully controlled since they are the highest in carbs. But non-starchy vegetables, like asparagus, broccoli, lettuce, tomatoes, cucumbers, celery, summer squash, iceburg lettuce, artichokes, green beans, bell peppers, and similar "salad" vegetables are "free". You can virtually eat as many as you want and not have an insulin spike. The starchy vegetables include potatoes (both white and sweet) and corn (and their derivatives like hominy). Grains should be carefully regulated also, but the more bran in them the less problem the grain is. (That's where they get the concept of "net carbs"). Pasta, rice, couscous, quinoa, oats, etc. are samples of these grains. Vegetables like carrots and beets have a little more sugar in them than the "free" vegetables so don't consume a whole cup of them at once. Do some research on the internet about diabetic diets, and you should get a good education on how to make a good meal. My diabetes management teacher said divide a plat in fourths. One-quarter is starchy vegetables, one-quarter is protein (meat), and the remaining half is non-starchy vegetables. If you are a vegetarian, take note that legumes are about half carbs, but they have so much fiber in them that it lowers the "net carbs". (It's like taking the carbs on the label and subtracting the dietary fiber, to get how many carbs will affect you, and thus where it fits in the 15 grams per serving measurement.) Fruit must be weighed to figure out how many grams of carbs are in it. Check out the National Nutrient Laboratories database. They measure things in grams. Check your nutrition facts labels on the foods you buy. It will tell you how many carbs are in a serving. Be sure to notice how many servings are in a package. Cans of vegetables usually contain 2.5 servings. How many total calories she needs to eat will also have to factor in to how much you feed her. Better to spread the meals out to have something every 2 to 4 hours (or whatever your physician recommends) than to eat three large meals and get low blood sugar before the next meal.
Since your mom is insulin dependent, you may have to serve her fruit as a snack between meals. For digestive purposes (to prevent acid reflux and indigestion and bad gas) it's better to eat fruit two hours or more after a meal containing meat and vegetables, and one hour before eating a meal with meat and vegetables. That gives the previous meal time to digest before adding more to the stomach. You might research food combining on the internet. The nutrition database can show you how many carbs are in what fruits, but beware of grapes, as they have too much sugar. She should definitely eat fruit, especially the dark red and blue colors, because of the antioxidants in them. Strawberries, raspberries and blueberries are examples. A half a cup should suffice, but check the database to see how much to serve for around 15 grams of carbs.
Yes, you'll have to be a mathematician for awhile, but once you make a list of the foods your mom likes, and get a set of measuring cups to regulate the size of servings, you can make some tasty meals that will keep her blood sugar regulated well. Keep a list of them on cards, so it will be easy for you or her to make a meal without having to calculate everything each time.