My mom is quite fat phobic. She had/has an eating disorder. When she was a teen she had surgery and was teased for the weight she gained since she couldn't move as much. So my whole life being fat was a bad thing.

Well my wife is overweight. About the same size as your gf. I've gotten comments when she wasn't around and I told my mom I love the way my wife is. As others have said you can also tell them ahead of time to chill out with any fat comments while she is meeting them. Best of luck with it all.