Strange behaviour - Help please?

Any advice please?
One of my Chickens has taken to sitting in the nesting box all day and all night. I'm having to lift her out in order to get her to eat and drink which she then does happily. 10 mins later she is back in the nesting box (not sitting on an egg).
Although she is 'mid-range' in the pecking order normally, the other chickens have started getting at her whenever they can.

Does sound like broody behaviour which is a blessing if you want to raise chicks and a pain if you want eggs.