I knew the sweetest dog named Jemma. In June, she passed away. I was asked to make something with her rain coat, and we decided on a pillow.
I wanted to make as few alterations to the coat as possible. I cut off the straps that would normally go around her torso. Then, I removed the straps that went around her collar. This separated the layers of the jacket, allowing me to remove the layer of batting between the top rain-proof layer and the bottom fleece layer. I also used this newly-separated edge to install a zipper into the seam I would be stitching to close up the opening.
With the straps removed and the zipper installed, I filled the pillowcase with a large pillow insert that I got from the fabric store. The zipper makes it so the pillow insert can be removed easily in case the coat need to be cleaned, allowing it to last longer than if it were a permanently enclosed pillow.