Chicken throwing up, having diarrhea, what is this?

[PersianPenName]

We have 7 bantam hens, and one of them spontaneously threw up a thin, watery liquid twice, and had very powerful diarrhea which was dark brown in color. The front of her chest is swollen, but she seems otherwise okay. Does anyone know what this is? Or how I should treat it?

 

[jerseygirl1]

I'm sorry, I don't know, but maybe a more expereicede BYC'er while chime in