One of our hens is acting strange

[brshooter]

Our RIR hen has not been laying for about a month. She is about 2-1/2 years old. Prior to that, she was laying an occasional egg every few days about a month ago. These eggs were very thin shelled and often broke in the coop. We were considering culling her, but she is one of my wife's favorites. She is still eating good, but I have notice she is sometimes distant from the rest of the flock and today, I noticed her posture. Her tail is down. Not up like the rest of the girls. Any thoughts?

 

[brshooter]

Rudy seemed to be doing a better when I locked them up tonight. Her tail was up and she went crazy for some scratch. Will keep an eye on her though.

She had always layed pretty good. 4-5 eggs a week. Really dropped off during the winter until we didn't get anything from her. She wasn't broody and no apparent change in disposition. We were talking about culling her and another of our older birds. We picked up 4 new pullets and when she saw them in the other coop, I think she figured something was up and actually started dropping a couple of eggs a week. They had very thin and brittle shells. They would often break in the coop. The yolks were still there so they weren't getting eaten. This lasted a couple of weeks and now she has quit laying again. Just can't figure it out. Any tips or suggestions appreciated.
Bill