Have you any foil dishes?
If so, cook using them!
We save up the good.ones for Christmas and.ither.times we don't want to fuss over the tins! So when you get good tins you could wash up, we do.
Christmas gone, bar the saucepan for gravy cz and the dish for microwaving the peas, all we did was wash the plates, etc. Last year we had roasted beg, in the foil of course!
If you have some foil tins do a pie or similar, a couple foils for dauphinoise potatoes, tinned marrowfat peas
Pudding do a bread pudding and custard. Or something???
It maybe that her mum couldn't cook, so her experience of home cooked ain't great?
Being.someone who was litterally force fed veg as a kid (the good old 70s children's homes!) and now can't eat "normal" veg.
Also if you have some old dirty foil dishes, screw them up and put in the bin, to make it look like you bought it.
It might be something that's mentall with her, so be kind, and see how.you can help your son, help her to get over it.
... If it turns out, her experience is just bad cooked home food, break her in slowly. If it's deeper, she may need.professional help.