The Semi-Homemade cookbook series is a good one for a casual cook. It's not haute cuisine, but there's enough variety in there to keep them out of a recipe rut.
Our teens' go-to easy pasta dish is Penne Arrabiata, which is a nice spicy change from typical spaghetti, and tends to be a bit cheaper if you can find a decent source for a jarred arrabiata sauce other than Rao's. (TJ's used to have a good one, but it has been discontinued. These days I usually buy the Culinary Circle version; it's decent, and usually runs about $2.99) The meat in this is loose italian sausage, and some hot pepper flakes (save them from pizza or chinese food deliveries) are needed as well. All that is needed is to brown the sausage and drain off the oil on some paper towels, then put it back in the pan and add the jarred sauce and a sprinkle of pepper flakes for heat. If you want to get fancy you can combine the drained pasta and the meat sauce in a casserole dish, top it with mozzarella shreds and bake it, but it's just fine dished out onto the pasta on your plate straight from the saucepan. We usually have it with salad.
Also a very simple one-pan meal is box-mix Chicken-sausage Jambalaya. It's best with dark meat chicken, pre-cooked and cut in chunks (in a pinch she could buy a few pieces from a deli counter & strip them, but just boiling it first will do, and that gives you stock to use instead of water, which is tastier), plus some sliced smoked sausage. It does need a large saucepan with a tight lid. Buy a box of Zatarain's mix and use it straight from the box as directed, or add some sliced green onion tops & bell pepper chunks halfway through cooking. Jambalaya freezes VERY well and is easily heated in a microwave.
FWIW, when I was in college I shared a house for 2 years with 3 other women, one of whose parents lived in the same city. Our agreement was that we would take turns making dinner M-Th. The girl with the parents in town knew how to make ONE thing: Hamburger Helper. Every time it was her turn to cook she made Hamburger Helper for the rest of us, then LEFT to go eat at her Mom's. After about 2 months of this we were ready to shoot her. Finally she got a decent job, so she tended to buy takeout on her night most of the time, but she still dumped Hamburger Helper on us fairly regularly.