This is terrible! Poor hen....
Reminds me of my situation with an older hen i had....
You see, this was my first ever hen that suddenly started getting bullied so bad i was worried for her. She was an old gal' and only laid once every blue moon...It was mainly all the roosters that were her bullies. She would refuse to mate with any of them apart from just one, which came with her a while back....the roosters didn't like this at all and started bullying her to the max, to the point where she would hide all day and all night and sometimes she would go without food or water for a whole day....
Ok so i let her free range, thinking my problems would be solved. Nope. The hens were also her bully, too. She became a mental mess, literally. She would run 100 miles per hour around the place untill she found somewhere to hide and she would stay there. For the whole day.
A hen that wont cooperate with the roosters is a danger to the flock, therefor they get rejected and cast out from the flock all together...were the hens and roosters will attack her at any given chance.
I ended up making a whole new pen for this gal' that i loved dearly. The very next day she passed away...rest in peace little girl.
There could be 100000 different reasons why your flock is acting like this towards your hen. When did you first notice this? She may not be cooperating with the flock, and wether you have roosters or not, it sounds like she has been rejected. Which can have 100 different reasons too.