That is not good in my experience, but I have seen hens come back from being sick too. Keep her warm, a sick hen can not get better in freezing temps. They tend not to eat when thet are sick or real cold. Try to warm her up and see if she will eat. I find that getting some fluid in them first helps, then try some food, a favorite treat, anything to get them eating. Give them some vit B12 in their water for a few weeks, like everyother day.