Oh Columella, I am so sorry. {{HUG}} We will miss her, she was a sweet (and tough) little dog.

(I expect it's little consolation, but... since she was fading so it may be possible she was out there because she knew it was close to her "time." I've seen neighbor's elderly dogs that were in bad shape take off from home, apparently looking for a place they could pass on. Might be a deep-seated dog instinct - you wouldn't want to die in the middle of the pack's den because your remains would foul it for them, after all.)