Hey Friend,
We're waiting on more specifics from you. "She can't cook- how can I make it better?" is no help to us. Cooking is far more complicated than that.
What does she make that's lousy? If you offer examples, maybe we can get specific.
We're generous to folks who ask for help- thing is- folks need to know how to ask for that help!
Are her hamburgers terrible? Perhaps it's the type of ground beef- whether it's fresh or frozen- or maybe she's cooking them too long and pressing all the juice out of them- making them dry.
Does her spaghetti sauce suck? Well, if so, we have an Italian mama here who's a real PRO at marinara sauce, bolognese and others- she will be a wealth of info to you!
Is her Thanksgiving turkey dry? Almost anyone here could offer hints to assist.
Her pies, cakes and cookies dry? Many fantastic bakers here.
Just ask, buddy! Just ask... There's no ONE remedy for ALL foods and dishes- so you must be specific.