How can I help my family stay together when we have a (step)daughter that is causing so much pain/drama

My husband and I have been married for 8 years. I have a son from a previous marriage and my husband has a daughter from a previous relationship. We now have three daughters together. I am so scared that I have taken so much abuse that there may be no point in return on my feelings toward my stepdaughter or husband. I really need help with this.
I that've fought, begged, pleaded and went above and beyond for this child to be part of our family and we, this family are the ones taking the beating.
To make a long story short, the past 9 years (including the year we dated) it has been tough dealing with my stepdaughter. She has been mean to her siblings including her stepbrother. She has made her dad cry with some things that she has said/done. She has abused her sister (babysitting, by not helping her to the bathroom and her sister pooping all over herself and she left her like that) because my stepdaughter was told no she was not getting to do something. For my sons birthday(a few years back), all boys were invited and she went joined in and taunted just him until one of his friends told her to go away and leave them alone. My son came in crying. Fast forward to today, this year 2010/2011-present. For homecoming a young man caught her off guard and asked her to go with him in front of the whole class and she felt obligated to say yes. She ended up telling the little boy no and her mom told her that was the lowest thing she had done in her life. She has also told her we were conspiring for her to live with us and for her to never go back to her house again (that was another time) Well I took up for her both times even after all the other mean stuff she has done to us. There is so much more, oh so much more. Since this time her mom I assume, felt bad and is now the friend again.
Aug. 13 was our anniversary and we were going to the movies and couldn't because school started and so much home work and papers we decided to do it another time.
In one week her driving she backed over a sprinkler, backed into a car and had a note on the winshield because of her parking. We tried to parent this situation but did not get through to her. The next week she lied to her SB coach so she would not have do whatever it was they were doing. Also to her dad. Last week she got to have her boyfriend over, we all had a great evening and they got to go to the school function the next day. Her phone was broken so I let her use mine to go to a school function, this is how we found the lie. My husband I decided we would go to the movies that night after they got back. When they arrived my husband told them what the plans were and she got mad cause she could not do what she wanted that night. She went in the room called her mom and said I was laughing because she could not go anywhere, she knew this would get a rise from her mothere. I wasn't even in the same area. But her mother has told my husband that I do all these things behind our daughters back.
This past week we find out that she was driving wreck less peeling out etc. in the school parking lot. The school called us and her mother ,which this week is where she was, and told of of the situation. We were very upset but nothing happened over at her mothers. We can't control things over there and it sure makes it hard to parent over here.
She has said and done things like telling me that she would not watch my kids "her sisters" and even if I make her that she will go to sleep and they wont be taken care of. She told my husband and I that she exaggerates to her mom about me when she is mad at me.
She hung up on her mother talked back to her dad all in the same day and still got to go to her bf's house. I don't understand.
My husband always says "I should have taken care Of this yesterday and we would not be in this situation now."
" I have a back like a duck, it just fools off my back.

Please do not get me wrong he tries when it gets really bad but I just think it should not get this bad before the problem is addressed.
He is a more logic person than I, but he let's things go that we wouldn't for our other children including my son.
I went to school to pick them up Monday and she decided on her own that she was not coming over here, which Is fine but instead if me dragging my sick daughter around and worrying about where she was , we could have communicated to her dad or he could have communicated to her mother about what was going on.
There is so much blame in every direction and I feel that everyone is at fault including me but I feel I am the only one trying to reach out for a solution instead of just pondering or not doing anything to help.

It has gotten so bad that I suggested to my husband that he and our daughter go to his parents until we figure all this out.
The last thing she told her dad was she did not want to come back here because of me.

Please help me figure something out for my family.

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