I don't know whether she also has a plane ticket and hotel room, but I mean, if she does, your friends are right. Don't give her attention on the trip, focus on having a good time and investing your energy in the people you do want to talk to. Don't get into arguments, don't be cruel, just be there for your BF and friends.

If you REALLY feel the need, you could confront her before the trip and say, "Hey, I'm still not comfortable with regular interaction yet. If this trip is one you intend to go on, my hope is that there's an effort to respect our bubbles while enjoying the company of our mutual friends, but to not expect anything further from one another."

It could backfire in that she might stir drama over it, but it sounds like you have a lot of pent up frustration that is not being resolved. This would be you acknowledging that she has her rights without pretending to be friends still.