Ok have fun. Yet if you ever change your mind, you & your boyfriend are still welcome always to come. Take this as a lesson learned. In the future you can’t make plans around her schedule anymore. It’s this date and this time. If she can make it, great. If not, maybe another time. Leave the ball in her court.
I have teens now. They don’t want to go everywhere with us. They have the option to opt out. Which majority of the time they do. Are we sad? Yeah, yet we understand this is the future of being empty nesters one day. Do we let them know we are sad? Nope.
The financial support is a separate issue here and should be discussed at another time. Just because you provide 95% of the support doesn’t automatically give you the right to force her or summon her to attend. If you feel it’s time to scale back in that department for her to gain financial independence, do so in phases. That way this doesn’t look like retaliation for not going on the family trip.