I think Disney is a great trip to let them take on their own. Especially if they're already very familiar with it. Safe/easy trans from start to finish being the main reason in my mind.
Only issues I'd think of are the usual ones with essentially getting teens a hotel room that you're responsible for. So, only you know your kid and her friends. Do you have concerns?
My 18 yo is a strict rule follower and a very routine person. She goes to bed early and gets up early. And we have our "ways" of doing Disney. My concern would be that her friends wouldn't like her by the end of the trip! lol Also, I'd be concerned if any of the friends coming along aren't big Disney World fans or are first timers. My D took a school trip at 16 y.o to WDW and couldn't believe how many weren't "into it" and how much time they just spent doing nothing and unable to agree on what to do. I remember her texting me upset because the group had been given maybe 4-5 hours of free/unstructured time and had managed to ride 1 ride. With the current situation of no fireworks, shows and other limitations, finding things everyone wants to do could be an issue. Make sure they have discussions ahead of time about how they want to spend their time.
Resort choice:
SSR is a very fun resort IMO for young adults because of DS access but it also means they are more likely to be out late / coming back to the room late, etc. I'm a cautious worrier. So, with me as the mom and planner, at just 18, being females, and assuming they haven't done much travel on their own, I'd probably shoot for BWV / BCV for max fun, ease of movement, etc. My girls love Epcot and HS and find those parks easy to just wander and stay easily entertained.
Any monorail resort being next choice. (Just depends on the group and how MK heavy they want to be.)
Make sure they have a ticket for every day with a hopper.
Make sure they are very up to date on whatever COVID rules and limitations are in place at the time they travel.
Make sure they know what to expect at the airport and how to navigate it.