I read an article that George Morris wrote not that long ago, and in that article he had a list of things that quallify one as a True Horseman.
The list had check mark boxes beside each listing, and one of them was "Holding onto the leadrope while your horse is being put down"
I choke up everytime I look at that, and I choke up even when I have to think about the day that Nelson and I will inevitably meet one day.
My MIL just had her Irish Draught put down, because she had tumors. And a dear friend just had one of her cherrished School Pony's put down because she coliced severely, only surgery would of possibily helped - since she opted DNR, she was layed to rest in her stall.
It is very, oh so very, very hard to make that decision, and go through with it and of course you are going to play the blame game - it is only natural. This is something that will remain with you till you cross over, but you can learn to accept it and move forward.
At least you loved your mare and gave her all the best during her life with you. For that, she thanks you. She thanks you, because you cared enough, because you gave her all you could, and because, you loved her. You treated her more than just a piece of property, and for that, she thanks you.
Now, you can check that box that makes you that much more, of a True Horseman.