If your goal is to get a mix of carbs and protein, I would recommend making your own shakes using whey protein and your choice of carbs. Most 'meal replacement' powders contain inexpensive carb sources, like maltodextrin. And these products can also be pricy when you crunch the numbers on price per serving.
My suggestion would be to buy a quality protein powder (PES Select and Myprotein Impact Whey are my personal favorites) and add your own carbs. This will significantly cut the cost per serving down, and it will allow you to manipulate the carb amounts to fit your wife's needs. Adding quick oats to a protein shake has been my go-to for years. You can also add in some variety with fruit and any other carb of your choice to obtain the proper carb/protein ratio