Libby, this post really hit home for me. I've known from the first time you chatted about your issues with your daughter that she was adopted from another country. I'm not sure I knew how old she was - if I did, it didn't "register."
I know I've been one advocating that you put your foot down. But Tricia's post, Carolina's post, and Linda's post made something in my slow brain "click," and I have FINALLY realized that what you are dealing with is NOT an "exaggerated" problem of a normal "troubled" young adult. And that's the basis of the advice most people are giving. You are dealing with an emotionally damaged child, not capable of having normal relationships, through no fault of her upbringing. That damage was done before you adopted her.
jcat's post put it made the light bulb go off for me.
I agree that family counselling is the next step, and that the therapist needs to be experienced in RAD. "Troubled teen" and "Rebellious teen" advice just doesn't cut it here because a child with RAD's brain is wired differently and the answers aren't as clear cut as "tough love." It's more about accepting limitations and working to gain trust without expectations. In that regard, I'm out of my league and cannot offer any advice on how to best go about dealing with the situation, other than what I've already given above. I really think that it has to come down to either accepting her flaws and all, or abandoning the relationship all together, which if I think about it now, only reinforces her ingrained belief that all people abandon her.
So before you make any choices or take any actions, please speak with a counsellor.
Of course, talking to a therapist for yourself and/or with Dave is always helpful, but "just" any counselor or therapist won't necessarily be properly trained to help you navigate this. 
!!!! I want you to know that I think you coming on here and "venting" has been the best thing for all concerned. From what I have read about RAD - which is new to me too - is that it really rears it's ugly head when the child reaches adulthood. I also want to say, although my daughter's issues are different from yours, is that my daughter also went from being a sweet, kind, caring, loving daughter and basically changed over the course of a summer - back when she was nineteen to twenty. The friend's she hung with, the partying, etc. etc. etc. Only until recently after this summer's event's has she started to see the light and understand and even ADMIT 
that she is selfish....... We are making progress but it took almost five years to even get started in the right direction. I think, until you all can get some answers and begin to totally understand the depths of what you are dealing with, you are at a roadblock.. of sorts. 
I really hope you are able to find a very, very good therapist to help you guide you through this maze you are all stuck in. Just wish you nothing but the best in this situation, Libby 
