Hi
Did you recently add these hens to your flock or recently acquire them? Moving to a new home or a new flock can cause them to stop laying, but the eggs that are in their system when you get them still have to come out, so they sometimes lay for a few days after the move and then stop. As others have said, moulting is another option, particularly at that age....we are starting to get into moulting season in the northern hemisphere now.
If she is egg bound, you will notice that she is distressed and it will often prove fatal after a few days, so you will see obvious deterioration. If she is spending a lot of time up on the perch, it may be that she is feeling bullied or lacking confidence to join the flock. That can be another effect of moving home if you have only just got her, but it can also be an indication of illness. How do the other birds interact with her.... you should notice if she is being bullied if you lift her off the roost and put her in amongst the flock. Do you have a rooster. Some hens will stay up on the roost as much as possible, to avoid his attentions, particularly if he is young and rampant.
