17 is almost an adult, she could leave home in the near future
Actually, she could leave home now. In fact, she could have left home a year ago, although technically she would need parental permission for this.
17 is still a child..not legally able to drink
It's legal to drink alcohol from age 5 in a private house. And it really isn't helpful to think of a 17-year-old as a child. Some government departments define anyone under 18 as a child but that's more so they can benefit from child protection legislation.
But I share your concern. And this comment:
I still used to let her know where I was and what time I was going to be home. That is part of being a mature adult.
Is spot on. As long as she is living with you it's just courtesy.
But then, the outcome of the Gillick case of 1985 was that parental rights should be transfered to the child as and when they become mature enough to take responsibility for their own decisions. It would be hard to justify saying no to a 17-year-old, I think. And this...
So if she ends up with a night in hospital or jail on her own
is a very valid point. At 17, she can be interviewed by the police without a parent present.
I would throw the ball back into her court. Get her to do a risk assessment - consider everything that might go wrong and come up with a plan. If she has had recent "incidents" it should be easier. Then go through it with her. Make additional suggestions, in a "have you considered this" kind of way. Emphasize you are just concerned for her safety and not trying to stop her having fun. Make sure she has some emergency funds - hidden somewhere it's unlikely to be stolen.
It's all in the planning. I've had to do loads of risk assessments and I used to hate them at first - they seemed so finicky. But I soon realised that by anticipating problems in advance they never actually materialized and everything went much more smoothly.