I ran into the same thing a couple of months ago. I didn't have any of the stash left from 10 years ago, so I matched the colors as close as I could. I first trimmed the area, then put the new small piece onto the hole (after placing a small piece of batting into the hole, and hand stitched the spot. She couldn't tell where - but I could! Her animal ate all the way through, so I had to replace the entire back. I then quilted it on the machine. It took me a couple of weeks, all holes are now filled and she's one warm happy camper once again!