Yesterday, I called the shelter and explained everything and was told that this peticular breed of cat, the female Tortie gets mean after they are spayed. We had you spayed because that is what the animal shelter required of us, as responsible pet owners. We didn't realize that it would change you forever, and that you would become so unfriendly and mean.
I have been avoiding posting on this topic, but I just can't let you think you are somehow responsible for her "getting mean."
First let me be very clear about something - Don't misunderstand me! I do think there was something wrong with her. From your description, it's very clear she was mentally unbalanced and a dangerous animal, and you did the right thing to have her put to sleep, but it wasn't caused by spaying her! I realize you don't know me from Adam, and that you have no reason to believe me rather than the shelter person, but I hate to have you think somehow you caused this...
I used to work as a vet assistant, I have been a kitty foster mom, had lots of different cats of different breeds, and showed cats for years. I cannot believe someone at the shelter would say such a hurtful and incorrect thing.
It is true that torties have a reputation for being somewhat, opinionated (just as orange tabbies have a bit of a reputation for being kinda doofy and brown tabbied have a reputation for being loving), but please, please believe me when I say that spaying her did not make her unfriendly and mean. Some breeds are more or less loving, but there is no breed where a particular color gets mean after being spayed.
I think these old wives tales start because mental and behavior disorders just aren't very obvious in cute fuzzy little kittens, and we usually get them spayed or neutered when they're 'teenagers' or 'adults', and it's just a coincidence that the mental and behavior disorders show up after the operation.
Losing a loved pet is hard. Feeling that you somehow failed is worse (I've been there). But Please, Please don't feel responsible.
I'm very sorry for your loss.