So she organized a celebration for herself but isn't paying for it? That's like inviting people to your house and telling them to cook, clean, decorate and bring the wine! You all are paying transportation, lodging, and meals, but you are getting a tee-shirt and a favor (which she has already told you about????). When you go out for her birthday dinner, are you going to be expected to chip in for her meal as well? What about her hotel bill?
I have no idea how great a friend this is. I don't know if you know the other "guests" (they aren't really guests - they are co-participants) well enough to discuss this.
But this situation is already way beyond any connection with etiquette. I imagine, when you get there, you will find out that a gift has been arranged and you will be told what your share is.
If you insist on going because it's already reserved and you've paid your non-refundable deposit, then I'd do something during the travels like write a poem about her or, if you can, write a funny song parody (take a familiar song and write substitute lyrics for her, which everyone can sing), or make a quick little photo collage of the 2 of you together.
Friends of mine planned a destination birthday for me - they all plotted with my husband, they drove here from other states, they reserved hotel rooms and made dinner reservations, etc. - but there was no gift. But THEY planned it - I didn't orchestrate it or know anything about it until they walked into my house, said, "Pack a bag, you're getting in the car with us and going to Boston." My husband was on board, had done some laundry and hidden the overnight bag in the closet, and I was set to go! I would never, ever have done this for myself and assigned everyone the bills to pay.