You need to start allowing her to sleep on her own. It may seem cruel, but crying it out is the way that children learn to self-comfort, and if they never learn how to deal with being by themselves in their cribs, they become impossible to live with. It is probably the hardest thing you will ever do up to this point, to let your daughter cry it out and learn to self-comfort and fall asleep on her own, but it will be worth it in the long run.
My SIL and her husband have a two and a half year old who has NEVER been allowed to cry it out. When she complained to me that she was getting no peace from her son, I told her what I said above and she acted like I said she should toss him out a tenth-floor window. She told me I was mean and cruel and unnatural because I advocated allowing a baby to learn to self-comfort. So...she continued rocking him to sleep, and now he's pushing three years old and STILL can't go to sleep without rocking. She made things much harder on herself, if you ask me, because now she has established this unfortunate habit and the child can't even begin to go to sleep unless one or both of his parents are there to hold him and rock him to sleep. Oh, and he usually wakes up screaming if he isn't deeply asleep when they finally put him in the crib and so they whole process starts again...rock, put down, scream, rock, put down, scream... Then again, she's also the kind of person who thinks it's "embarrassing" when a child cries for more than two seconds...but I digress...
The long and short of it is -- it's not cruel to let a child cry it out, it allows her to learn to find comfort in different ways, it will be easier on you in the long run, and there are plenty of other ways to spend time -- quality time -- with your daughter. But you might be better off dealing with it now or you will be stuck still rocking her when she's in kindergarten.........
(I should also point out that my son, now 10 years old, was transitioned to not being rocked pretty quickly when he was a baby. Once he was in his own room and his own crib, that was the end of the rocking all the way to sleep most of the time. And he cried it out for one or two nights, learned to comfort himself, and was fine after that. And he's a lovely, well-adjusted, self-confident fifth grader now, with nary a "complex" because of his "cruel" parents...)