Definitley a variety of meats, to include the lean meats, and some fattier meats, plenty of fish (watch mercury levels though, canned tuna has less than tuna steaks).
Lots of veggies. If you can get your mom to go to the store often, you can have her stock up on fresh veggies. The problem I have with them is that they don't stay fresh very long.
Sweet potatoes, broccoli, baby carrots, peppers, asparagus.
The least processed oats you can find, although the more processed the less cooking time so find a balance (like Quaker rolled oats).
Some yogurt, cheese, cottage cheese or milk to get some dairy in for calcium.
If she won't go for supplements like protein powder maybe you can at least talk her into some fish oil pills or flax oil, along with a vitamin and mineral supplement. Tons of health benefits from those EFAs, and it's almost impossible to get an optimal amount from whole foods.
Oh, and some natural peanutbutter and nuts too (unsalted).