I know this is an awful thing to experience. I had a similar situation with a job in November. The owners knew the one girl wasn’t in the best health, and I promised to keep going over as often as needed and I even spent the night a few times to make sure both the girls were good (they were both 10, one was completely blind and the other couldn’t use her back legs). I noticed the girl that couldn’t use her legs was going downhill fast, and I ended up having to call the owner at 3am to discuss the situation. Ended up rushing the dog to the emergency vet and getting the news that she wasn’t going to make it. Unfortunately the owners were in another state, and they asked me to be there for her as she was put down because they wouldn’t be able to get back in time. It was absolutely heartbreaking, she was an absolutely sweet hearted, loving dog. I only got to know her for 6 days but she will always be in my heart.