Remember, that just like you... she will take just about anything during this tiring time! :) So don't feel like you have to be a pro at cooking.
You can mix just about anything into "goolosh" type dishes.
Anyways, tuna casserole (or use can chicken if they don't like tuna) is very easy. Cook noodles first and put in baking dish, put in two cans of tuna, 2 cans of cream of chicken soup, and lots of shredded cheese. Bake 25 minutes at 375 degrees... add French's fried onions on top for the last 5 minutes. Fantastic, easy to reheat, easy to freeze. Put this in two smaller dishes one to freeze and one to eat right away, instead of one big dish. Add cooked shredded carrots if you'd like. Use orange cheese too and the kids will never know the difference! :)
Also, you can do the same thing with anything. We cook noddles, put in large dish (or 2 small dishes), add cooked hamburger, lots of cheese, any kind of veggie that is already cooked, spaghetti sauce and bake that until bubbly... since everything is basically already cooked. Another easy supper to reheat or freeze.
Good luck!
Also, its just helpful to have cut up fruit around too. Healthy and good to eat, but a new mom will never have time to cut up strawberries or apples.