IMO a child should never have to apolgize for feeling uncomfortable or voicing that they are uncomfortable.
Think of all the other things in this world that can/will make her uncomfortable. If you chastise her now for this, what is she NOT going to voice about later?
Being rude is another issue. That probably deserves an apology. Could a 'meeting' be brought about with the other mom, daughter and your daughter with you? Apologize for the rudeness and discuss the uncomfortable situation.
Constant talk of fatness, body image, food can and does often lead to eating disorders. I have a co-worker who's daughter has been hospitalized since January for anorexia. She is 15 and has been battling this since she was 10. She had a chubby friend who was picked on and who's family kept wanting her on a diet, etc. Hannah didn't want that and stopped eating.
You don't want to go through this. Something like that destroy your child and your family. Your child stating that it makes her uncomforable is actually a very mature attitude. The approach, maybe not so much.
