Boyfriends friend being disrespectful

Hi there, sorry I know this sound a little immature and High but it’s what it feels like.

I have been with my boyfriend almost 3 years. He had a best friend who sadly passed away and he was very close with him and good friends with his sister. I don’t really know his friends sister and she does not know me.

However apparently she made a really rude comments about my weight to my boyfriend to which he or so he said defended me. I am curvy girl but hardly obese. He wouldn’t tell me what was said but think it’s was really quite nasty and he said she was laughing about me, this girl herself was very overweight a few years ago. I don’t know about you all but I could never do that. As it turns out she then sent a picture of my boyfriend and I from a tagged photo on holiday of me in a swimsuit with him and sent laughing emojis. My boyfriend tried to hide that from me but I found the picture when he replied to defend me she tried to back track and say she was only joking and that she has a funny sense of humour but I did have a nice face. I have been trying to lose weight but went through an emotional time over the last few months with a miscarriage I’ve been so upset but what she’s said. I called my boyfriend going crazy I am PMT but he said I’m overreacting and she’s being jealous and I’ve not to be silly. What do I do should I confront this girl? I’m also really annoyed at my boyfriend? I have been going to the gym for the past few months nearly everyday but weight takes a while to come off as you all know. I know feel so low and worthless. Any suggestions of a move forward would be helpful or am I overreacting and should use this to catalyst my weight loss journey? Thanks in advance of you made it through reading this.