Replying a bit late, but OP how often do you do your food shopping ? If you can switch the meat at least to once every two weeks, hopefully if you have a shop that does deals on about to expire meat on a certain day certain time (show up first!), that’s how I get my roasts (it can be very large sizes and eye wateringly expensive still with the reduced price, but the reductions are usually quite good and batch cooking as you know is much more cost effective.
Does depend on the size of your freezer, but that can also be helped : if it’s large, you can pop the meat in for whenever ; if it’s smaller, need to cook it that day as it will reduce the space it takes (just roast it, cut up, then the day you eat it adapt accordingly with extra spices or whatever, as it will taste best if you pop it back in the oven to reheat (I usually have something else ready for the oven at the same time, nothing too complicated, it can be just a load of chips (as you have 3!) to go with the meal, to save on energy).
I don’t even have a fussy eater, just a small budget and I feel much better this way as I do stress about proteins. Luckily mine likes eggs, but I feel guilty anyway if too much. Also lentils, pulses stuff in general are sadly out.
Anything homemade I also feel better I admit, it’s great she loves pizzas, as, as PP have mentioned, you can ‘cheat’ loads with the sauce, and as she seems to like veg she’ll do fine likely with the toppings (you can suggest a bit of roast as a topping also, it’s really an advantage to get the huge ones).
Veg I buy in bulk again large bags of frozen ones, so I can vary a little, and they tend to be cheaper and no spices
Sounds like you know all this though really☺️, you just need to get out of the ready made meals temptation and get back to home cooking. I personally don’t do the ones that take huge amounts of time to be honest. If in a rush and you don’t know what to do for her, your fajitas suggestion is great, and also you can get a panini etc maker for really cheap, same for smoothies makers (less than £10 at home bargains type stores and those can make for equivalent of pizzas, and very nutritious for smoothies if that happens to work. For the boys stuff like buying a ready made korma sauce for rice as those can be cheap and quick to make if you have to make 2 meals that day. (I think if I home cooked absolutely everything I’d go insane!)
Best wishes, you can do this!