I agree with lots of the reassuring posts on here, that it sounds as if your daughter's got her her screwed on right, that the non-standard hours are not uncommon for that age, and that since she's managing to hold down a job and study, there's lots to be proud of and the night-owl tendency is not something to worry about.
Having said that, I would recommend just keeping an eye out for any sights of depression since there is a correlation between night-owl hours and depression. Not that strong a correlatlation though, so not something to be overly concerned about.
But what's taken me aback is what a hard time you're getting from so many posters!
Whilst 9-5 are universal hours, the majority of people who aren't on shift work, work mostly during the daytime (those on shift work mostly change between night and day, and few night-workers like working nights,not to mention all the scientific evidence that it's not good for health). And many of the most productive leaders of society get up early. So it's not strange that you'd be concerned.
And at 17, yes she's old enough to choose, but no, she's not so old that you should talk to her if you feel she's living her life in a way that won't help her. For goodness sake, even adults of mothers are entitled to gently give their opinion without having that kind of 'control freak' accusations that you've been getting.
You sound like a good mum, and I think your worrying is a sign of caring, not of control freakery. I don't think you need to worry though, and it sounds like you've done a good job raising a daughter with a good work ethic and self-discipline: I struggled to manage distance learning in my early 20s and certainly wouldn't have been self-disciplined enough at 17.
So please don't listen to those poster who are accusing you of all sorts. But it sounds like most of us, including them, agree on one thing - you should be proud of your daughter.