I homeschool and for my 6-year-old-daughter her melt down zone comes for math. She GETS it, but she doesn't "like it" so it's like pulling teeth to keep her moving along on her math lesson. This leads to some burn-out, because I can't just let her not do it. This week, all week I cracked the whip trying to force her through her chapter, letting her skip some super tedious parts ONLY because I knew she understood them...and sure enough: When I gave her the test at the end of the chapter, she flew through it perfectly because the test is shorter, and she gets a sticker and the gratification of "another chapter down". But the daily grind is hard for now.
Don't get frustrated. Just urge her as you are. Discipline tantrums, but don't let the overall homework scene get too ugly, but don't let her skate either-it's a balance. Give it some time. I never used rewards regarding teaching my kids discipline, but now with school work, I do find incentives help a lot....like "when we get to the end of your ___Book, we'll go to a movie" etc. Maybe offer her a fun activity with you if she does this work for a whole week without complaining. Good luck!