"She's not into drink or sex as far as I can tell ...."
Count yourself lucky for that alone. First of all you can't 'control' a 16 year old. You can be there for her, advise her, but she's turning from child to adult and as you know yourself, these are some of the most confusing and difficult years.
When my daughter was almost 16 she met a boy a few years older. She did actually ask me if she could stay over at his, but I said 'no'. Not because I was trying to stop her from having sex because I knew I couldn't, but because she'd known him for five minutes, from what I knew of him I wasn't that keen tbh, and he still lived at home and I knew absolutely nothing about his parents, home life etc.
I explained to her that once they'd been dating for a while and she'd got to know him and his family better then fine, but it was too soon.
The following weekend she was staying 'at a school friend's' house, only I got accidentally got locked out of our home. Tried to call he to come back with her key (no answer) so on a hunch I drove round to the boyfriend's house and of course, there she was. As I tried to explain to her, it was the lying that pissed me off. She'd asked my opinion, I'd said no and she ignored it anyway, so why ask? Needless to say the relationship didn't last. He turned out to be a right little shit in the end, but that's another story.
Not long after that she accidentally pocket dialled me and I could hear this whole scenario of her and a bunch of friends 'running' away from somewhere and effing and jeffing like navvies. There had been some sort of fight or confrontation, lots of shouting with my dear little daughter at the heart of it, one of the boys was clearly worse for wear and it was obvious they had all been drinking. I could hear the whole thing like it was a radio drama. Made me realise what they got up to.
She is now a 25 year old Science teacher in a secondary school, having gone through college, degree, teacher training etc. She has a steady boyfriend who has his own business and she is truly delightful daughter, in every respect.
Yes she could be a worry and a pain in the arse when she was 16 (my son was even worse!), but it's par for the course.
As Judge Judy says "you know when a teenager is lying because their lips are moving."