Something doesn't seem right about your story. The mother is supposedly a JW but is letting her son and your daughter sleep together in her house, even though she herself has been disciplined in the past for the same issue. If she is a JW and doing this, then she's a JW in name only.
You said that they've made up a lot of lies about you so how do you know if anything you've heard about his family and the goings on in their house is true? How do you know if this business of him owning guns and being violent is true? Who told you that they were sleeping together?
If your daughter is 18, there's not much you can do except behave rationally and maturely. The tone of your post makes it seem as if you are (understandably) indeed being a bit hysterical and controlling (sorry), which will only drive your daughter further away.
I certainly wouldn't go running across the country after her if she hasn't asked you to come. If she wants her papers, then send them to her. In addition to her getting what's legally hers, she'll have to give you her address so at least you'll know exactly where she is (if you don't already).
If she's doing chores and taking care of a child, maybe that's a good thing. She'll get to see that being away from home isn't the picnic she imagined. If her boyfriend is being possessive and controlling, maybe she'll tire of it and contact you about getting her out of there.
If she doesn't graduate...that's her problem. She'll have to get her GED or go to High School again next year. If she looses out on her scholarships....too bad. She'll have to apply again. She must be a smart girl so she'll have to figure out what to do. This is not your problem.
It seems to me you're working harder at this than she is. You've given her the idea that she can come home anytime, which is nice of you but I'm guessing that (like most teens) she doesn't appreciate what she had or how much you did for her. It sounds as if she's got the upper hand here and has the idea that she's doing you some kind of favor by contacting you. If you are as freaking out about this as much as you say, it may be that if you've been overly involved or overly emotionally invested in her live, you've given her the idea that she's pretty special and she may be a bit spoiled.
If it were me, I'd let her know that you are there to help her if she's in trouble and that you MAY be open to the idea of letting her come home but now that she's moved out in this manner, things will be different from now on. It may shock her to see the change in your tone go from desperation and panic to one where you've "dropped your endo of the rope" and handed it all over to her.
If she actually asks to come home, I'd lay out some ground rules. Make sure she knows that it's not a done deal and that if you do allow her to come home, you're doing her a big favor , rather than the other way around.
You've had some big losses and are quite vulnerable at the moment so you're probably letting her walk all over you. She'll appreciate you more if you stop being somewhat of a doormat.
