Can someone please tell me the best sedentary weight loss diet for someone suffering from spinal stenosis?

My wife is 26 and suffers from spinal stenosis and she has gained a lot of weight in the past year and it has impacted her self esteem terribly and she doesn’t know what to do. I’m of course here to help and I’ve tried mentioning keto to her multiple times and she just doesn’t want to do that. Idk what else to do but I do know that her weight is not helping her condition at all and I’m just running out of ideas and so now I’m just worrying about her all the time. I want her to be more comfortable in her own skin again like she was a couple years ago. She hates herself now and it’s so sad to see her like this