I recently had to put my 33 year old mare down. She had horrible heaves, was skin and bones, and wasn't aware of her surroundings. Did I do the right thing?
The last gift we can give our beloved companions is freedom from suffering.
You didn't think about yourself and your own emotional pain, you thought only of her. Bravo.
If more people thought that way, maybe we wouldn't have so many animals selfishly kept alive for no other reason than human ego.
A true horse person knows when to let go.