Euthanizing his dog was rescuing her again.

[Catherine]

Alan and his partner rescued two dogs during the pandemic. The dogs became a special part of their lives. They thought they had many more years. Suddenly one night, Kahlua had trouble breathing. At the vets they learned that it was congestive heart failure. Treatment options could only prolong things a matter of months. They didn't want to let her go, but letting her go rescued her from the pain she was in. It gave her a painless end without further suffering.
It rescued her from life that had suddenly become unbearable. It was the loving choice that rescued Kahlua one more time.

https://www.cbc.ca/news/canada/euthanizi...-1.6822418

It is a hard decision, but it is the kindest thing we can do when a pet's body can no longer sustain life. Trying to buy more time is not kindness.
Releasing Kahlua before she suffered more really was rescuing her from pain and fear.

I was faced with a similar situation when I was caring for someone else's cat. He collapsed from a massive heart attack. He was not going to recover and he was suffering. I wish I could have kept him alive until my friend returned so she could say goodbye. I couldn't do it to that beautiful cat. He was frightened and in pain. I held him while they brought an end to his suffering. It was the only thing I could do.