I don't think this is at all unexpected.
-Any kid who has been through what she has been through will be messed up. She doesn't know how to be normal. That takes time, lots of time. Years of effort on her part and on your part.
-Your wife's issues mentioned up thread, that's not going to make this easy, ever.
-After people get comfortable, best behavior slides from the forefront of people's minds. She, and the rest of you all, are probably not constantly putting your best foot forward constantly, and it has led to increased strife.
You're in this now. If I knew all of the details and had your ear before you got custody, I would've advised you against it. But that's an option that is gone. You stepped forward out of the blue to solve a problem. Now you've finally seen how problematic that problem is. Thing is, if you back out now, you'll have messed this girl up even more than had you done nothing. From my perspective, you're karmically pot committed here. It will improve over time, but just as she needs to learn how to be a normal kid with a normal family, your family has to learn to accept her 100%, fleas and all. Love is unconditional. You cannot let yourself regret this decision. It will not work out if you do.
I would recommend 2 therapy sessions a week, one for her and one for everyone together. Every week. If cost is an issue, start a gofundme and link it here and I'm sure several of us will chip in. I would also recommend that you find whatever patience you can, because this will be a bumpy ride for a while coming. And finally, I'd edit your updated thread title. Heaven forbid that kid stumble across this thread and read that.