how long to broodyness last or how to break a brood??

Im due to go away in a couple of weeks, and have someone to pop in once a day to chuck sit...
my problem is one of my hens went broody about 2 weeks ago, and showing no signs of coming out of it, I have tried to break it the last three days by kicking her out of the nest and closing it off, but as soon as I open it back up shes back on it...

shes been fine with me making sure she comes off for food and water, and has been fine over the last few days excluded form the nest, just wondered how much longer it will last, and iff to be worried about leaving her with a sitter? and if I need to do something else to try to break the brood? (preferably something non-stressful)