My 85 year old mother had a minor heart attack due to COPD complications. She is refusing to allow others to cook meals for her. She lives alone. She eats well for breakfast and lunch, but generally has very little at dinner. She is Five Foot 3 inches tall and weighs only 103 pounds. She is still very weak and tired from the heart attack but does not want anyone to help her.
She doesn't have a reason to get into the kitchen except for fixing small, survival meals. Remind her of those stick-to-your-ribs dinners she used to make. Tell her how much you miss them. If she says it's a lot of work, tell her you and ______ (outsider) can give her a hand.
Another option is for you to start making those dishes and ask her to supervise to make sure they taste "just right." Fumble and bumble a tad to give the appearance of helplessness. Working as a team might help relieve some of her depression.