Your kid has done well. I think that the best thing you can do is to let your kid know that you appreciate all that they have accomplished, are proud of the person that they have become, and that you are letting them own their own life and all the responsibility that comes with it.
Then do it. It sounds like your kid has earned it.
Many of us have stories that could be told but want to put them to rest. With our No. 1 there was no slackoff at all even after he had accepted an offer to attend. That’s in part because he had a couple of major EC’s that kept him busy, and on one of them his coach (debate) made sure all the debate team did their homework! With our No. 2 there was a letdown that led to an inferior but barely passing grade in math but that course wasn’t critical for her, since she had been admitted to art school.
While maintaining academic focus is important in senior year, I would pay more attention to the summer before college and to social activity as much as academic. The student may well slack a bit but make sure s/he isn’t running off to out-of-town concerts, parties, etc. Students should really have an R&R period in summer but not a running wild one. Freshman year can be very challenging, moving to a new place, having a totally different routine, and an exacting curriculum. Make sure your student is physically rested and thinking about the opportunities head.