I sympathize with you! I raised 2 step daughters, one was only 8 when she came to live with us full time and the other was 10. The 10 year old was terrible and we never got along while she lived with us-which was til she went to college.
One thing I can tell is that I had my own daughter also, who is half sister to these girls. She was about 4 when they moved in with us. My relationship with my own daughter was ENTIRELY different than with the step daughters. If you ever have the desire to have your own children, don't let your feelings for the step daughter scare you off.
These girls are all young women now. My daughter is 23 and the stepdaughters-there were 3 altogether, the eldest never lived with us - are all in or near their 30's. I have some advice as someone looking back on the step child experience.
Looking back, I wish I'd been more patient and loving to these girls. I think that would have changed much of the turmoil our family experience for years. My husband and I nearly divorced over all this and I felt like leaving many, many times over the years. I stuck it out in hopes that when the girls left home, my husband and I could at last have a good relationship and I didn't want my own daughter to end up a "step.'
I know this doesn't always happen in blended families but as these girls got older, somehow their opinion of me changed with maturity. They have little children now and I'm Grandma and they all moved to be near us so we can be part of their lives. I love the grandkids and, honestly, the past never even comes up. I can truthfully say now that I love these young women as much as I love my own daughter.
I realize if I went back in time, maybe I couldn't do anything differently. There was a mess of emotions involved and my husband was no help at all, due to his own guilty feelings about the girls' "real" mom and the divorce. The girls played on that guilt and they never really gave me a chance.
It took quite a bit of forgiving for me to let go of the past but I did it and I'm glad I did. Life seems so good now, compared to what it was during those year.
Don't think either that you just need to get the daughter grown up and the troubles will be over. She will get married, have kids, there will be holidays and family celebrations, so you will be thrown in with her and the entire family on many occasions for the rest of your life. It's best to try and make it work now so you have no regrets later that you didn't try harder.
Try reading Wayne Dyer's book The 10 Secrets of Success and Inner Peace or some of his other books. They really helped me.
There is hope! I wish you all the best.