Absolutly no punishing find out what she is upset about.
I agree dont force her my kids are 2 and 4 and they dont always eat. Somedays they wont eat breakfast or lunch and very little supper. Somedays they eat like crazy. My son is 4 and weighs 37 pounds. That is a normal weight for that age. She will eat when she gets hungry. I say sat plate in front of her she either eats it or don't.
If you force her to eat she will associate eating as a form of punishment. You could be setting her up for a lifetime of eating problems. My daughter is 53 inches and 54 pounds. She is just naturally skinny. And don't make the mistake that kids need to eat everything on their plate. Some kids prefer to eat less but more often during the day. Again, don't force her; just make sure she has access to healthy food.