Diaherra/cold - how do I treat this?

[Zinnia-Hen]

One of my hens seems to have come down with a cold. She isn't completely out of it, as she still wanders around the yard with her two buddies, but she seems tired and has loose, yellowish/whitish, typical diaherra looking poops. She does eat, just a little less. No eggs, but she hasn't been laying regularly in a month or two so I don't think that is something to be concerned about. So far I have electrolites in their water and she's in the run with the two other hens, taking it easy. The two others, by the way, seem to be okay. Their droppings are a bit like hers, however. The rest of my chickens do not have this.

So, I was just curious, how do I take care of this? I've never really dealt with diaherra in birds before.