Does she get an allowance?
If so, have her come up with the money to go?
I noticed that DGDs were more reluctant to spend "their" money than their Dad's or mine!
I guess it depends on who is paying. If it's that important to her - and she and her friends are willing to spend "their" money on it - let them!
If you are the one "directly" paying for the ticket and snacks - then I think YOU are the one that gets to choose where to go.