Kiev still broody

Kiev is still broody, taking every opportunity to sit in the nest box (whether there is an egg there or not). Every day we take her from the nest box several time a day and encourage her outside. She stays out for about 20 minutes before heading straight back into the nest box. Yesterday at about 4pm I closed the door into the run so that she couldn't get back into the coop. After about an hour she seemed quite upset, pacing round and round the outside of the run trying to figure out how to get into the coop. This broodiness has been going on for some time now, I fear drastic measures are necessary.......