The concierge staff at CR are absolutely wonderful! Breakfast is usually cereal, fruit, and pastries. Snack is usually finger sandwhiches, chicken wings, and a veggie platter. Desserts are usually cookies, mini cakes and such. Avoiding gluten can be difficult, but if you plan in advance it shouldn't be too much of a problem.
If you haven't already, you should be recieving a letter from them about planning your stay. When you receive it, take the opportunity to call them and talk to them about your MIl's restrictions. (Try calling between 10 and 1, they seem to be less busy then as everyone is in the parks!) Most of their treats are made in the hotel, either by the bakery or by the california grill, so they should be able to work something out

I also agree with the previous posters advice of, make as many advanced Priority seatings as you can, and notify as many of them about the restrictions. You may also want to start to take a look at the menu's for the different restuarants so that you will have a good idea of what places your MIL will have lots of choices at.
I absolutely love the CR concierge staff- they are some of the most wonderful people

I'm sure that they will be glad to help you! Enjoy.
--heather