The minute she unzips her backpack, the gripes start to flow -- her teacher is too unfair, the work is too boring, her classmates are too bossy. She'll continue to nitpick until bedtime, when you'll realize that her homework is barely finished.
Battle Plan Suggest that she visualize putting all the unhappy parts of her day into a big box, and invite her to tell you about them once her homework is done. If she starts to complain before her assignments are completed, remind her that complaining isn't allowed until she's finished her work. Once she has, let her moan and groan to her heart's content.
That said, don't automatically discount your child's bellyaching. If she frequently doesn't understand the assignments or has a staggering amount of work, help her figure out what's expected and check in with her teacher about the level of the homework.