I think make sure she knows you’re on her side, and that you don’t value the opinion of those people. “I just don’t understand why they are so critical of your body and feel the need to comment on you all the time. You’re a healthy weight, and you look incredible, its just bizarre that they behave that way. What is their problem? I wonder if it’s jealousy, or maybe they’ve been brought up to be insecure about their bodies, such a shame to be like that, I’m glad we’re not like that” etc. Keep trying to reinforce that this is their issue, not hers.