Most Helpful Guy
Well first of all, you should be aware that many girls have a hard time severing emotional ties. I've seen girls feel guilty or show concern for ex's that were totally abusive to them, even though she broke up with them. Girls are just the type to always feel sympathetic towards people. This is why girls always want to know what their ex's are up to. Personally I think lots of these girl, while their intentions most of the time are innocent, are playing with fire. I'm in the camp that ex's should be erased out of your life as much as possible, unless of course they are a friend or something that you dated. So based on just her conversation with her friend, I wouldn't necessarily be overally concerned. Would I like hearing that, no, but would I break up with her because of it, probably not.
Now the part I find strange, although I don't know much about the situation, is that she wants to go alone. I can understand why she would be staying in the same house. I knew a girl who dated a guy, and was friends with his brother, and both their families were extremely close. It was like they were related, so it was common from them to to be living at each others parents houses sometimes. So that doesn't bother me. I feel like if she had nothing to hide, she would have no problem with you coming. If anything, she would prefer you come for emotional support since its obviously going to be a crazy and hectic experience. The only reason she might not want you to come, is because she feels that you don't really have a relationship with any of the families and that it would be awkward to have you there, but still I'm not sure I buy that. It's totally acceptable to bring your SO/spouse to a funeral.
Ask her why she doesn't want you to do. If the answer sounds like a bunch of BS, then that will tell you a lot. Even if she still insists she go alone, I'd be curious to see what her behavior was like afterward. What I'm trying to say is I agree you should be cautious. But I'm not quite sure I would break up a 3yr relationship so fast. Give it some time and continue to investigate.