I got home from an out-of-town trip this morning, and one of my runner hens was reluctant to stand up. She stayed laying down while she ate and drank, doesn't seem to be in any pain and is shaking her tail a lot. She has done something like this once before and eventually laid an egg. Is that probably what's going on? It's been more than an hour, and I have her in the bath tub in warm water. What else should I do?