YANBU to say no. I would NOT like this and I would NOT allow it. IDGAF if she is 18 next week. She is still very young, and she is still living at home. If she is not 18 til next week, then she is still at school. She is also not an adult - not yet. As pps have said, she is financially dependent on you, and she is still living under your roof. A child does not just automatically become an adult on their 18th birthday. Maybe legally, but not mentally or emotionally or financially! They can't look after themselves financially!
When she was 16, my DD wanted to go to a concert with an 18 year old friend, 100 miles away, on the train, with a change half way, and a half hour wait for the connecting train. This 'friend' was well known for going off with blokes and disappearing with them, and leaving her friends to get home on their own. (No matter what they were doing or where they were.) She had done it to my DD twice. We had to go and get her at 11pm from somewhere twice - as this girl had ditched her.
We let it go the first time, but after the second time, I said she is not going out with her again, and she certainly was not going to this fucking rock concert 100 miles away, in the hope her friend wouldn't ditch her and fuck off with some bloke she met. YES she was 16, but if she been only just turned 18, I would not have allowed it, if she was still living at home - and still at school! No way!
Say a firm NO @WagonWheel1234 your daughter cannot go. It's irresponsible for you to let her IMO. Especially on her own! It is NOT controlling, it is good parenting. Letting her go (alone) is not.