I found that when I was working a lot, meal prep on my days off solved the problem mostly. I'd make a big pot of pasta sauce, cut veggies for meals and salads, precooked proteins and rice portioned out for meals, etc. That way it was quick compilation and reheats with very little actual cooking on workdays. My feet hurt and I was tired, even though I was only slightly overweight.
Even with the kits being simplified, there is still going to be standing on feet for the minimal prepping, reading and following instructions, and some actual cooking. This might work for someone like you but likely not your sister I think. I'm sure the extra weight makes her feet hurt even more after a long day.