I had a great mare who did fine into her mid or late 30s (she came from an auction, and we didn’t know exactly how old she was). We had her for 14 years. Then, she suddenly got aggressive with my husband, whom she’d previously worshipped, was picking on my pony with whom she’d always been best buds, and couldn’t seem to figure out where the hay was when it was right in front of her. Of course we euthanized her.
I know my mare’s life had gotten to be intensely unhappy, and I think it’s the same for your mare. You and I both gave them the hardest gift there is–a peaceful end to suffering. Please don’t second guess yourself for even a minute.
Rebecca