chicken seems to want to sit all the time

My 8month old chicken seems to want to sit all the time over the last couple of days.  she is coming up and walking  for her treats and eating properly.  Just seems after a couple of min on her feet she needs to sit and rest.  I have picked her up and taken a look, and can not find any thing obviously wrong with her.  She never layed eggs on a regular basic, but did have one yesterday from her.  Any Ideas?

dont think she is broody as keeping out of nest box.  she out and moving around.  just not much.  its very windy here today, but the chicks dont seem to care..  she just seems unhappy.

yesterday she seemed to have improved alittle, but this morning she was the same.  walking a little before sitting down.  think i might have seen a slight limp.  have looked at her feet and legs and dont think there any thing wrong.  she was happy for me to touch all her legs.