I agree that this can be very frustrating on both ends, for you and for your daughter. My suggestion would be to break your daughter's homework up. Do it for 10 mins. then take a break. Go back to the work after maybe 10-15 minutes. I would just break it up and remind your daughter she can do it. She might not believe in herself, but remind her she is capable. Also, let the teacher know. Maybe your daughter's work is either too hard or too easy. Let the teacher know what is happening at home. Maybe your daughter can do 10 math problems instead of the 20 or 30 assigned.

Hope this helps!