What do you do when someone in your house is on a diet?

I live in a multigenerational home with my MIL, husband and kids. Recently my MIL received the news that she has diabetes and high CO2 in her blood. She has decided to go on a very low calorie diet to "reverse" the diabetes. Her doctor knows and says it's fine but she looks awful. She has all the signs of slow metabolism and talks often how carbs and sugar are "bad" foods.

I'm triggered as fuck