I don't know...I tried everything already suggested and more...then I finally did what my parents did with me...a few weeks ago, I gave up! May not be the right solution for everyone...but it seems to have worked for my parents at least...I eventually earned a Ph.D. even though I NEVER did any homework after second grade (until graduate school!)!
I do agree that you need to identify the reasons your daughter is having problems with homework. Is she also having problems with her "in-school" work or is the problem limited to homework? Does she have a physical or mental disability that is affecting her ability to learn the material?
I did all that with my son...he's making honor roll every term (at a school for gifted academics)...and all the testing indicates he's more than capable of doing the work. I finally concluded that, just like me, he simply does not WANT to do his homework and instead of applying all that brainpower to just getting it out of the way, he applies it to finding excuses NOT to do the work. Crying, yelling, more crying...sharpening his pencil and then breaking it so he can sharpen it again...going to the bathroom every five minutes..."I'm thirsty/hungry/tired"...you name it, he does it to avoid doing the work. A few weeks ago, his homework involved writing six sentences using his spelling words...it took him five hours and he still didn't finish it!
I finally figured out that what he wants is for me to do the work for him...he knows that his education is important to me and figures that if he pretends to have difficulties, I'll do the work for him to keep him from failing. A few weeks ago, after two weeks straight of 5-6 hours a night on homework I finally told him that he could do whatever he wanted to do about homework...do it, don't do it...the choice is his and so are the consequences of his choice. In the last few weeks, he's gone to school without his homework several times...and has had to go to study hall instead of recess to finish it...and come home with a discipline report from his teacher (that results in consequences related to TV, video games, and playing with friends).
He hasn't gotten any better about doing his homework yet...but we haven't had any six hour crying/yelling sessions either! He knows that he won't be allowed to stay at his special school with all his friends if he started earning failing grades...and I'm no longer willing to spend every moment together fighting about his school work and will put him in a different school if he doesn't choose to take responsibility for his school work.
I don't like this solution...I feel like a failure...but it just doesn't make sense to me to continue allowing school-related problems to destroy the peace in my home and turn my child (and I) into emotional wrecks...there are just too many educational opportunities available to make us miserable trying to make this one work if he isn't willing to cooperate!