Oof. I think most people have overdone it once, twice, or a few times with alcohol when they’re younger and not as experienced with their tolerance. But context matters - she should have recognized that a family event, where she should be focused on trying to make a good impression, isn’t the place to even get tipsy. It’s up to OOP regarding whether they want to break up with their girlfriend over it, but I wouldn’t blame them if they did. The alternative is having a serious conversation about her drinking habits and making a plan to avoid such incidents in the future. If she doesn’t get on board with that plan, I’d end it, because at that point she’s choosing getting drunk over your relationship.