Stella's Pneumonia Treatment

We adopted sweet little chihuahua named Stella last week and we all fell in love with her. Since bringing her home though, I noticed something was wrong; she has been very lethargic, labored breathing, etc. I took her to the vet yesterday and found out she has pnumonia. The adoption center won't help with any vet bills, and the only other option they offered was to return her, which I would never do. We definately cannot afford the treatment and x-rays at this time so I figured I'd give this a shot. We don't want to lose our little Stella!