Frozen Mucus on hen

Hi! We just came home and the first thing I did was check on the chickens. It's been REALLY cold today (4 degree high), but not windy. When I looked at my white EE hen, I noticed she had frozen mucus on her butt. I took her in and cleaned it off- it was frozen and looked like a long drip of mucus from the vent. Could this be from laying or should I be worried? She just laid the first egg I've seen from her yesterday. She seems a little slow and lethargic, but in the cold, it's hard to tell if that's being sick or just keeping warm. Let me know if you have seen this in other birds- as a symptom or as a natural part of egg laying. Thanks!!!