Until the age of 18, you are the boss of her - end of!
I have been looking after 12-18yr olds for 14 years now and firm but fair works really well.
If she is grounded, I presume she doesnt have her phone or a computer or tv in her room? If she does, it is just a curfew and as effective as a wagging finger. And before she goes on about human rights and all of that nonsense, you could always open her eyes to the children of the same age in Japan who have just lost all of their possessions due to the earth quake and would kill for a roof over their head, let alone go to a party.
Could you put it to DD2 (and her Dad, to win him over if he needs it - hopefully he shouldn't!) that you can't trust her to stay in her own/another person's house... how on earth can you trust her in the middle of a concert on a beach with several hundred strangers, most of whom will probably be a lot older than her? Put it to her Dad as a safety issue - to her it should be a (justly deserved) punishment.
YANBU to stop her going. My parents regularly left us at your DDs ages and we certainly never had parties.
No, she can't go. Phone the Dad who got the tickets and tell him why she's not going, offer to pay for the ticket (take it out of her pocket money) if he can't re-sell it. Phone her Dad and tell him to back you up.
I don't even understand why your ex got her tickets to the festival, does he not know what goes on at festivals? Is he just massively naive? I would never let my 14 year old go, not even if she was an angel.
All my friends go to festivals and I am no prude, but there is enough drug taking, heavy drinking and unsafe sex for me to know I would never allow my 14 year old child. 18 and over, sure no problem, but 14?
She sound rather spoiled TBH, either that or having emotional problems. It'd not a 'strong character' OP, its a selfish character.
I just told my DH as he has been to T4 on the beach a couple of years ago and he was all raised eyebrows that your ex would buy your daughter and a friend tickets.
LDNMummy - T4 is aimed at that age-group - Only under-12-year-olds are not allowed in without adults. My DD2 has been twice, with older teenage relatives ( she's 12 now, so was 10 and 11 when she went, relatives were 15) and has always had a fantastic time. It's not overnight and the bands are mostly teen- appeal.
If you ring her dad and explain what has happened would he back you up? I agree that it is a fair punishment in the context. You allowed them a chance to be respoonsible and they weren't, how do you know they will behave at the beach?
(It is a 'teen' festival, have not been but I imagine the security is very strict, the t&c on the tickets for eg says the only food/drink you are allowed to bring in unopened smaller than 500ml bottles of water)
YANBU - she shouldn't go. It's her fault if her friend isn't allowed to go if DD isn't going, not yours. If her attitude is bad now, it will be even worse when she realises she can effectively do as she pleases and not get much of a punishment for it.