I feel like I put my dog to sleep when maybe I could have done more?

If she was not eaten or drinking, she was probably in pain. I feel your pain because I just lost my beloved German Shepherd too. Elka was only 10, and had a horrible type of cancer. It was a month ago to this day, and when I remember her, I think to myself, a month ago, I still had my beautiful shepherd. You did the right thing. Unfortunately, dogs get old, and there is nothing to stop that. I am tearing up right now, and I suspect I am making you do the same thing, so I'll stop there. It sounds like she was suffering, so you did the right thing,