What would you do in this situation

(anyone can answer but if you’re over 18 that helps too) So, my sis calls me and we were talking. She is in VA with her boyfriend/fiancee at his family reunion. She was saying how is family doesn’t like her and all this stuff (when it’s not true. She is a very likable person). Basically, she said she was gonna break up and call off the engagement since his family doesn’t like her. She said it was like being in high school all over again where people don’t pay any attention to her and it makes her feel left out. She doesn’t talk to him and tell him how she is feeling cause she thinks he won’t care. She has this mindset where she automatically assumes the worse of anything like “oh they don’t like me cause they aren’t talking to me” type thing. So I need some advice and what you people would do. Would you dump your boyfriend/fiancee if his family didn’t pay any attention to you? Can someone give me some words of wisdom that I could pass along to her to at least make her feel a little better and find a better reason to dump him and not for the stupid one she gave?

With him, she is happy and not depressed like she used to be and if they break up, 1. I will have to try and stop her from trying to kill herself (yeah she was saying she was gonna kill herself after she breaks up with him, if she even does) and 2. it will be like I lost a brother/friend so it would be hard for me too. I’m just lost and don’t know what to do.

Yeah I know its possible that he could dump her because of how she is acting but I don’t think he would or at least I would hope he wouldn’t.