If the extra expense won't be a sacrifice for the family then I vote for the one she wants to go to. She'll remember it as special not always wondering how great it could have been if she had to go to the one she didn't really want to go to. She'll have other choices to have to do without her wishes so if this one can be granted then let her have it come true. It's really a small thing to us but major to a girl her age. I have raised four teen girls and now raising my 16 year old niece. Little things like this give them so much confidence in their social world.
Just want to add, forcing life lessons just for the cause of having them see the reasoning won't work. Most teens know the family situation and know what can or cannot be granted.