Help! My rabbit refuse to use her nest box!?

my rabbit has already pregnant for 27 days. I used to let her wondering inside the house, so she already pick a place to build her nest, and start building it. but it was outside her cage and in a place i don't think safe (and it is not safe). so i gave her a nest box inside her cage but she refuses to use it! she just rampaged it and being grumpy all day.. she insist to go out of her cage. what should i do? i know it's almost the big day but i don't think she's gonna use the nest box..