She wants to go to her friend's sibling party in another town some 100 miles or so away. I know the family & they're all really nice and trustworthy, including the party host. However it's a student party (ah, the memories, but at least when i went to student parties I was a student myself and not 15!). It's also a long way away and she'll be staying there overnight.
I've said no (she had already told her friend I'd said yes, somehow when she first mentioned it she thought I'd reacted positively whereas I was just thinking about it). So now she's upset.
Was I right? Am I being unreasonable?