Are you her husband or her father? Both of you are adults and unfortunately, you are not her father, nor do you have the power to control her or her behavior. You can only control yourself and how you react to her behavior.
You aren't dealing w/someone who is thinking like an adult at the moment. She's thinking like a 16 yr old. They rebel against any authority that they think you hold. I can assure you that MLCers will take the easy way out when given ultimatums.
So, daddy, what are you going to do if she goes out during the week and misses curfew? Going to ground her? Think again, she's going to do what she needs to do to find her lost self.
I wouldn't say another word to her about her going out and staying out. You've stated how you feel about her doing these things, now leave it alone. Oh, and by the way, if you state that she can do whatever she wants except cheating...you are opening a can of worms and just to rebel against you and what you stand for, which is an authority figure, she just might do it to spite you. The more you demand she stop doing something, the more she's going to do it. It's called rebelling against an authority figure and you may just remind her of the person who stunted her emotionally a long time ago.
Well, they all rewrite history and her perception of you and how you made her feel is very real to her because they are her feelings and perceptions of how things were. Maybe they aren't true and maybe they are just a wee bit. We each have our own perception of how things are going in our relationships and sometimes we don't realize that both parties may see things just a bit differently and right now, her glasses are totally dark and your glasses are foggy, but they will clear up in time.
You may have been working on yourself for the last three months...but you've got a ways to go. Ultimatums will not work w/MLCers. Step back and leave her alone. I want to pound this into your mind so that you'll remember this...you can't control what she thinks, says or does. You don't "let" her do anything because she is an adult and she's going to do what she needs to do. The only thing you are going to do is focus on you and how you react to her behavior. You need to just leave her be. Yes, I know her going out is bugging the BS out of you, but again, you are not her father nor her "employer". She is not your daughter or your "employee". She has free will and she's going to be making a lot of bad choices along the way, but she has to grow up and learn the lessons she missed early on in her life. At the moment, she doesn't want your help and she needs to dive in head first in the MLC roasting pan and work through her crisis.
Just remember, the more you tug on that rope, the more she's going to focus on rebelling and she will not be focusing on her internal work of self.
There is a very slim chance that if you back off now, don't make demands and just leave her be, she may not file in January. There are times that they will threaten filing to get us to back off.
Keep the focus on you and leave her be. Having them in the house is difficult, but it can be done. Visit HaWho's threads. Her h is living in a "dorm" room in her home and he's been in the MLC oven for quite some time. She's managed to do an excellent job of keeping her sanity.
Also, you might want to take some time and educate yourself a bit more on MLC and depression.