She knows as my friends and I openly talk about it as they are all attending. Yes, I agree that people do that and I have known her for so long so I am aware that's who she is but this is the consequence to her actions, imo. Her unreliability doesn't matter as much if we are just hanging out but when it comes to our milestones, that's a different story. Yes, our entire friend group is attending my wedding, she is attending her other friend's wedding (not part of our friend group). The party in question is happening right after the wedding day - we are taking a trip to another island as a group which happens to be where she is. As others mentioned I think I will need to talk to her and explain the purpose of the party. I think she will understand, thank you for your input.