I'm sorry to hear about your wife, that sounds awful. I also had post COVID issues, I couldn't get out of bed for a month and was very low energy for three. The doctors did nothing for me but luckily I have now recovered on my own. I tried eating lots of vegetables and lean meat (as per official nutritional recommendations) and it made me worse. I remember building up the strength every day just to chop the vegetables, eat and go back to bed. When I told my Doctor they dismissed it. I recovered on a diet of fatty red meat (1-2lb per day), milk, cream, eggs and fruit. The diet could be a timing coincidence but on the other hand maybe my Grandmother was on to something feeding me beef stew when I was ill as a kid.
I also get acid reflux with excessive fat. The key is to eat it with enough protein and carbohydrate in the same sitting and not to lie down after eating. Fat also makes protein easier to digest and of course protein is key to building yourself back up after fatigue and inability to exercise. I would avoid some fats such as sunflower oil or vegetable oils (except olive oil) which are inflammatory. Coconut oil is good because it contains lauric acid which is anti inflammatory. I also avoided starchy carbs which tended to knock me out and eat them only in small amounts paired with easy to digest sugar such as fruit juice. Simple sugars from fruit are not inflammatory despite bad press. It's essential to keep blood sugar up because if you are already fatigued its easy to get hypoglycemia. Consuming fruit juice before meals considerably reduced my post meal fatigue. I went from unable to stand up after eating to feeling better after eating.
Current dietary recommendations are the same for everyone and implicitly assume you are slightly overweight and sedentary, consuming a caloric excess. In America many people die of obesity related diseases and dietary recommendations based on the epidemiological data reflect this. When you are weak and frail in bed it amazes me that Doctors still recommend the same diet based on this data. It took me so long to realise why salads and lean protein were making things worse. I needed more calories! More protein, fat, sugar, all the 'bad' stuff to build myself back up. Of course I'm assuming your wife has lost weight while ill as I did and this doesn't apply otherwise.
There will be a law suit over how CFS patients are currently treated: https://www.virology.ws/2020/07/15/trial-by-error-nice-on-ex...
You might want to follow it. I will be.