I think she should have her room how she likes it. It's her space. I wouldn't like someone coming and telling me how I can have my space. Just put the rule she's not allowed to have sleep overs at your house, etc, if her room isn't clean. She still has to help with the chores with the rest of the house to earn her rewards, but her room is hers.
Lay a few ground rules, maybe, that her bed needs to be stripped once a week(hygeine purposes) and there's no dishes to be taken into her room.