Linda, I just hate knowing how awful kt is to you. I think it was always so that she was the stronger of the two and she would be the one to lash out. I'm sure that she thinks it makes her powerful, but all it means is that she is and always will be bio-monster's victim. You gave her and WM all you had to save them with an open heart. I guess my feeling is that she was unsaveable. It doesn't devalue anything you did for her, it's just the way that it is. She can talk about suing you all she wants, but that is just about the most preposterous thing I have ever heard in my life. It's something a child without the guidance of an adult would do. No attorney would go near that with a ten foot pole.
If you are going to bother letting her get her stuff, I agree with DDD about taking photos so that there is a record of what you hand over to her. I have to be honest and tell you that I didn't give M much of anything when he came back for his stuff after what he put us through. I cleaned out his room - which I'm sure you did long ago - got rid of things like school-books and garbage, saved a few things that were precious to us, gave ALL of his childhood toys away, gave away his video games, set aside his Eagle Scout stuff for when he was mature enough to get it, sent him his clothes and called it done. He had delusions that he was going to take furniture and bedding and household items. Oh, h--- to the no!
If I were you, kt would never be back at my door. You're absolutely right that she has abandoned her things. If you feel that she honestly owns anything that would be of any use to her that is still in her possession, I'd box it up and send it to wherever she's at and then, as you have mentioned before you might do, I'd move away. I'm sorry that kt had such a horrible childhood, but there does come a time when you have to say that she is no longer a child, and she is the only one who can make a better life for her. Lashing out at you is going to do nothing but make that harder for her.
I know that you feel you don't love her, I really do. I also know that you can love her and let her be without you. She's triangulating, and if she can't triangulate you into the equation, then completely cutting her off may be the last gift of love that you ever give to her. She'll either use it to better herself or she won't. But you and I and all of your family here knows that she will never be a loving caring person so long as she has her bio-monster to feed her anger, and you to take her anger out on.
I'm so sorry. This is the part of parenthood for some of us that is nearly unbearable. But sometimes it's the only way to make a recovery for yourself. In the end, you're all you've got. Treat yourself right.