I agree with everyone else here. You Must put your foot down!
First, Forbid her to play with ~Anything~ until she cleans the cage! NO afternoon snack, either! When she comes home from school, the FIRST thing she has to do, (after taking off her coat, and dropping her book bag down), is to the clean the cage, NO if's, and's, or but's! CLEAN the cage! If she throws a tantrum, TELL HER you're going to get rid of the bunny! If she throws a tantrum, then DO it! Then ground her from her toys!!!!
Jeez lady, you're raising an unruly child. Get a grip on her Now, before it's too late!