I am new to chicken raising. We have 4 girls we raised from chicks. They are about 5 months old now and not laying yet. Two days ago I let the girls out for some free range time. Our girl named C3PO who I believe is a Plymouth Rock went running with the others then stopped suddenly and lay on her side with her feet in the air. I went to carry her back to the run and she got up and ran back by herself. Later that night when the others went inside for the night, I found her laying on her side again under the coop. I brought her inside in a crate for the night. Its been very cold out so I was worried about frost bite. Also, if she can't get on the roost with the others she would be really cold all night. I looked her over and could find no sign of injury. She is perky but not as feisty as usual. She is eating and drinking just fine. Her poop looks normal. She just seems to not want to use her legs. I started her on a vitamin supplement that the local feed supply recommended. What else can or should I be doing for her? Any clues to help me figure out what is going on with her? The other 3 hens seem to be fine. Thanks for helping a newbee!