An extreme problem needs an extreme opinion.
You probably won't like what I have to say, and that's ok.....it's just the best way I've handled things in my life.....
I was a teacher so I've dealt first hand with ADHD, ODD students.
You need to home school her, for at least a year, just to see if it helps. I've had a lot of students whose parents have done this, and the ones who do it right, it has helped more than any drug I've ever seen. She needs extreme structure, set consequences for her defiant actions, and more love than anything. She probably feels really rejected because of her father, and by you because you married a great guy (it sounds like) and had a child with him and now she's jealous. You and your husband should take control of your family and your little girl. It's going to take a lot of work. I suggest not putting anything else on your plate, freeze time and fix the situation before it gets out of your control.
Read some Dr. Laura books, she saved my life and my family, but you need some tough skin to swallow what she has to say.
Hi Ashley, Read your message and I feel for you. It seems your daughter has some ASD also,( Autism Spectrum Disorder) My son is 13 and he is Autistic. He has a mind of his own and his favorit words are "I want!" or "I need it!" 8 is a tuff number on any child with special needs. Maybe I can give you an example of how I deal with my son when he has his tantrums. And they are very bad tantrums and this is always. I make a deal with him when he asks for something like a new movie (C.D.) or a toy, a game for his play station or Wii game. He has to show me he can behave by cleaning up his room (picking up his toys) and or listen to me and his teacher and do a good job at school. Then I give him a couple of choices...1) a road trip to any where he likes (or I like and I choose where thats more affordable) 2) Go out to eat at his favorit fast food like McDonald or Burger King. The road trips can be to a special store he likes (or I like) Wal-Mart, Dollar Store or Game Stop. Game Stop is a game store you can return used games and trade for other used ones. Its' the best place for these kids with the game boys and play-station. Don't have to spend a fortune on new games. These things can be a reward once a week, every 2 weeks or once a month. It all depends on your budget. I like to do it every two weeks.(thats pay day for us) He seems to enjoy this deal and looks forward for the reward and the trips. It's not 100% affective (but I'll take 40 to 70% any time) but it helps sometimes. And he needs to be reminded constantly. I have to keep it low key by not raising my voice with him cause he will react the same way. I like also to take time to play tickle with him to be closer and show my love to him. He loves it when we have tickle time. I'm thinking if your daughter can communicate and make choses. Maybe ask her to give you a list of 5 of her favorit things she likes and pick the 2 less inexpensive and work on gaining that reward. The dollar stores are a great place for inexpensive toys. Sometimes that would be one of my chose to take my boys on a road trip. But she has to gain it by following the rules and behave. One time I was upset with my son (13yr old with ASD) and he refuse to listen. So I took a garbage bag and put all his toys and games in it. He was very upset and scared I was going to throw his things away. Well, that changed quick for that moment. And he started to pick up his mess. I kept the garbage bag near by just in case. He did comply. He realized I was serious. But this is a battle every day with him. He is getting better but very slowly. It's very hard for me to go out with him most of the time. I try to do most of my errands during school hours to avoid any arguments or tantrums when we go out shopping. Don't know if it'll work for your little girl but maybe something might click and help you out. Also, my son is on medication but I give it to him at night cause it makes him sleepy. Plus I only give it to him when he really needs it. Try and count to 10 when you loose it and remember she is a sick little girl and she needs you as much as you need her.. No one else will be there for her. Love her, hug her and show her you care with alot of affection. She's reaching out to you. Remember chose your words wisely. She is learning from you and your actions. Good luck! And keep the faith!