Don't be too hard on yourself. It is very hard to figure out what is best for each animal. If she didn't make it, I would have felt bad for not putting her out of her misery.
If they are responsive - talking/clucking - giving some sign that they are fighting, I try to assist as best as I can. I am sure I have left some go too long when I should have culled earlier. She was definitely a fighter, so it came out ok this time.