My wife is scared

For the past few weeks, my wife has been eating round about 2000 calories, I don't mind this but she does. She has a minor fear of gaining weight but that's not the main problem. Her main problem is she thinks she's being incredibly unhealthy for eating 2000 calories. She still eats her veggies but she doesn't go out for walks as much anymore because she is sick and grieving, now she is horrified at the idea of eating 2000 calories and it's gotten to the point that any snack or meal she is given, she's horrified to eat it. What should I tell her to reassure and calm her down?

Edit: Thank you everyone for the advice and help. I deeply appreciate it. (: