Hmmmm I'm on the fence with this!
An "open" invitation on social media, was it to a large group on snap chat or a public post on Insta?
Personally I would offer to take DD and her friends and then wait nearby for 3 hours in the car. I probably wouldn't let her go without at least one good friend going with her as she doesn't really know the other girl.
We would agree a "safe" word she could text where I would know she wanted to leave immediately!! And would go and knock on the door to get her if she text it.
Let your children make decisions and learn to be streetwise is part of being a parent.
I remember once my DD (13) text me from a park one evening to tell me that some of the kids had alcohol and was I ok about it. I asked her what she wanted to do, and she wanted to stay. I drove to the park and just parked up and waited for her to call me to collect her.
Yes it's boring and cold, but it's giving your child a chance to make adult decisions but with you as a safety net.
I was always the parent that would pick her friends up even if it was out my way to make sure everyone was safe.
When DD had her 13th birthday she invited over 30-40 people from her school to our house. Only one kid's mum wanted my number to phone and text to ask me countless questions. I felt really sorry for her kid, who turned out to be as anxious and nervous as her mum.
It's a really fine line between helicopter parenting and neglect, especially with girls.
It's a bit like when they want to go to school on their own when you think they're too young. You let them go but unbeknown to them, follow at a safe distance!
It's difficult OP and you're going to having countess other worries as she hits her teens!