Rebecca, you did everything right by her. You were a good parent by what I read, you sought counselling and it also looks to me that you and your husband supported each other.
I really wish that I could say that I have been there, done that but my little girl is only about ten.
I would have to say that she may need some tough love. She may also need to figure out seeking help on her own. As a parent that is hard to say. As a child that grew up in an environment completely different than hers, she won't openly think she needs help.
You will unfortunately get blamed for a while until she can grow up and learn.
I have seen a lot of this first hand with family and friends and peers in the mental health community. My little sister and I had a pretty good up bringing but she rebelled, hard core and sometimes I am embarrassed by how she talks to our dad. Now she is married, we are in our forties, she has settled down a little.
A lot of people I see, they seem to not either want help or they don't want to help themselves. The later is the hardest because they usually just accept a label and let a doctor do whatever the doc wants. Which is not always the right answer, self advocacy, good support and time.
Be open. Do not push. She's an adult now. Love her, let her know she is loved. The rest will come with time.
I am not a doctor or professional, just a kid who grew up with severe abuse. I am disabled and have been actively involved in my mental health problems since 2014, before that I didn't even try. Now I have control and I say to my doctors I am willing to do what it takes but we have our boundaries.
Another unfortunate thing is the generation thing. I have seen way too many kids now that feel that they are entitled to everything and everything right now. They tell adults that you cannot do that, like she did with her grandmother. And some of that is our fault, some is our parents faults but mostly it is our American culture's fault.
I am almost sure that it won't be long before the dog is back with you because she will come to see she can't take care of it. Just be patient.
Don't give up, don't push, just love.. All we need is love..