I sort of had the opposite issue my last year at home. I also "skipped" my senior year to go to college but hadn't actually graduated yet, but I was 16/17 that year because of where my birthday fell. My dad and step-mom told me if I was ever going to be out late (and it was nearly always for work), that I needed to find some place to stay. They used the rationale that they didn't want me out driving late. My state also had a driving curfew if you were under 18, except if you were working. It made it difficult a couple of times though when I didn't have somewhere to stay after working late.
How late is she going to be out? Does she have concerns with night vision or safety with driving so late or the area she would have to drive through to come home? Does your state have a driving curfew for teens under 18? Have you met her boyfriend's parents? How old is her boyfriend, by the way?
Personally, I think teens aren't going to wait for the opportunity to sleep over to do things if that's what they really want to do, so I wouldn't necessarily let that aspect be a huge influence on my decision. I think a lot really depends on the maturity and responsibility of the kids and what their reasons are for wanting to sleep over somewhere. I do agree with a PP that if she is living with your mom, that the decision should probably be more of hers to make.
Although there are many 18 year olds who do not act like adults, they are adults and can make their own decisions. If she is still living at home/ with your mom, then it is totally reasonable to set whatever rules you/ your mom wishes while she is living there. Understand though that she is also free to move out if she doesn't want to abide by those wishes.
From personal experience, going to college early is a great opportunity for teens to experience more personal responsibility while still having the guidance and support of living at home. It can be a little tough when presumably all the friends she will make at college will be older than her and many of them will be on their own and not having to follow parental rules. Every kid matures in different ways and handles the pressures of college differently. I would have a discussion with her about what the expectations are of her while she is going to college and living with your mom. Are you paying for the dual enrollment credits or are they paid for by the school? If getting her diploma is contingent on passing certain college classes/ maintaining a particular GPA, make sure she fully understands all of that as well and knows that she has to take the initiative to make it to her classes on time and get her work done and ask for help if she needs it because the college isn't going to be reminding her in the same way teachers do in high school. Sorry, I know a lot of this isn't exactly what you were asking about, but my point is that she's basically doing something a year ahead of her peers. I'd focus more on making sure she's prepared for everything to come and knows you are all behind her. Keep the lines of communication open, talk to her about any concerns and expectations that you have, and give her a little freedom to make her own choices. She's obviously smart if she is going to college early, and from personal experience, when a parent shows trust in you, that alone is a huge motivator to make good decisions.
