You lay down the rules, very clearly. Very, very clearly. "When you live under my roof, and I am financially responsible for you, you will live by my rules. If you are not willing to live by my rules, then I will ask you to go live elsewhere, where you can be an adult and take responsiblity for your own life. If you do X, Y, or Z, which are against the rules, I will give you 3 weeks, until Sept. 17, to find a new living situaton." And then you put her stuff outside and change the locks.
She will not take you seriously. You will ask her to leave. You will stop paying for college. She may even move in with the boyfriend, get pregnant, and ruin her future. But if she is not forced to take responsibility today, she will have this exact same problem 10 years from now.
My mother did not force my brothers to take responsibility as teenagers. Now they are 45 and 51, and never progressed. They skate by. You know many other people whose siblings are exactly like that. Forcing her to grow up will be painful for you, but the alternative will be painful for her, forever.
I know that you already know all this stuff, M.. And I'm sorry that you're going through this. My oldest is 13. I realize that I may also go through this one day. Dr. Laura counsels people on this topic, and she has encouraged me to be brave enough to face it when it becomes necessary. I wish you well, and I hope that your initial "rules" conservation is well-received. Blessings to you.