We've been talking about this in our house a lot.
Tickets on sale tomorrow...somehow DD has got the impression that I would be happy to buy a couple of tickets for her to go with a friend rather than with me 
.
She's a very responsible teen - turns 15 in September but...
a/ I'm not really happy for her to go with a friend on their own which means I would also have to buy a ticket and hang out on my own like Billy no mates
b/ Other option is that I escort her and friend there and back but don't go to the actually event - 1.5 - 2hr journey each way for me to facilitate this. I'm not thrilled with this idea and whether XH would agree to this anyway is doubtful. I think it's only fair to get his opinion as I'd want him to ask mine if situation was reversed.
c/ she wants a bigger than usual birthday party this year...nothing elaborate but social group has expanded so we've been looking at hiring a hall...I don't have a bottomless budget. We're also going on holiday in October which I still need to save a bit for.
So AIBU to give her 2 options:
1/ I get 3 tickets - they can go standing, I'll get a seat or standing but try not appear as though I'm with them 
but no big birthday party
2/ We go together, just the two of us
3/ I'd you don't like either idea we don't go at all and you can wait until you're old enough to go on your own and pay for your own ticket.