Are you dealing with a lot of what's listed here? - http://www.centerforthegifted.org/cntpub_under.htm

If so, you might want to try counseling and either scaling back or bumping up the work. Your DD could be totally bored from the homework or find it completely tedious and irrelevant. She might not see the point of doing the homework and not motivated to do it.

IF this is the case, I feel your pain!