poorly hen?

These are classic signs of depression caused by a likely egg laying issue.

If she has been laying extra large eggs or soft ones she could be egg bound.  You can sometimes feel them upwards towards the back.  If she is going to the nest frequently but not laying it can help to warm her rear end in a warm bathh which helps to relax the muscles.  Isolate her in a box and keep warm indoors may help too.  Try googling for advice on egg binding. 

If no egg is passed it could be a more serious problem and eggs could have fallen into the body cavity causing peritonitis which is a very serious condition requiring an antibiotic injection from a vet.  If her undercarriage feels hot and bloated this could be the problem and the sooner you get her to a vet the better though recovery is entirely dependant on the severity of the infection and often proves fatal.

Ex bats are prone to laying problems in their second year though she doesn't sound like she's an ex bat.  What breed is she and is there anything you can tell us about her breeding history?
HF