i'm sorry too, if i sound rude saying this but,
It is really hard for anyone to hurt or kill a pet. i could never. and no matter how expensive one of my chicks is, i would do ANYTHING to save her. if i were you, i would consider other options besides culling her. i have some ideas, but i'll let the professionals judge me first
In my opinion (and this is just an opinion), it depends on your choice. Personally, I consider quality of life. I raise my birds for eggs and meat, so I make sure that I don't get emotionally attached. Finances are another hard truth. Can one afford to spend hundreds of dollars plus on a bird that only lives 2-3 years?
I absolutely understand about a pet, however. My cats are my family, and I would go a far distance for them. If, however, their quality of life is going to be short and poor, I think it's kinder to end the suffering. For example, last month I took my cat in to the vet, and her best prognosis was heart failure, her worst was sepsis. Either option was bad, neither gave her much time. She was obviously not happy, being barely able to get up, so I cried, and opted for euthanasia. On the other hand, I spent $6K trying to keep a young cat (only one year old) a chance to live after renal failure. I couldn't afford the $20K for a kidney transplant, and he passed away regardless, but I tried.
The right or wrong decision is up to the person who is in the situation. I don't think there is an absolute right or wrong that applies to everyone in a situation like this.
If your bird can live a decent life with a crippled leg, then let her live. In my case, where I can't reasonably pamper a single bird, she wouldn't have a good life in with the others. In the case of a pet, she might have a good, long life, even though crippled.
Sorry for the long post.