I'm so sorry for your loss. I, too, know the pain of losing a pet. They do become our friends and family and they leave a huge hole when they go.
We had our 14 year-old boy put down in May because he was in constant pain and couldn't walk anymore. Afterwards, my Maggie wouldn't eat for about a week. She'd eat her treats and whatever handouts she could get, but she wouldn't eat her dog food. Eventually, though, she seemed to understand what was going on and started getting back into her routine.
I hope Coco starts eating soon, and I hope you're all able to grieve for Sadie in your own ways and start to move forward.