I need some help with my rabbit please!?

My rabbit has a hutch with a wire part and a part I put straw or bedding in there for her to sleep in. She always goes to the bathroom in her straw the very next day after I just cleaned it. Aren't rabbits supposed to be clean animals? Is this normal? I have two other rabbits and they don't do this at all. They always keep their sleeping area clean. Is there anything I can try so she won't go to the bathroom in her sleeping straw all the time. Also it's not hay I am putting in there because i have a hay rack that she can eat hay out of. Thanks!