Thank you all for your kindness and support. Shadow had a very, very long life, and I had a suspicion due to how much she was slowing down that this summer would be her last, but no amount of time with her could have ever been long enough. She was such a funny, gentle, intelligent friend.
To quote my dad, "As a natural herder, she knew her job was to keep track of where each person in the house was at any time. She took that job seriously right up to the last day!"
I like to think that she is still keeping track of us, like a good herding dog, watching her "sheep" and waiting to see us again. I will always, always miss my dark-eyed, cock-eared buddy.