You are not a murderer, if she kicked the egg out and wasn't sitting on it any more then she wasn't getting any response from that egg. They can hear the chick inside the egg the same as we can but they hear better, Something must have been wrong with both of them. It happens and there isn't anything we can do. Mama knows what she is doing. If she has given up on the one you have left then I say you should too. I think I told you about the 2 from one of my broodys last year, she was able to take care of the first that hatched[kill] then i stepped in and felt like I had to rescue the second one, well i should have just left it alone and let her take care of it too. It never did look like full term chick, and died 5 days after it hatched. I'm sorry for this but it is just part of the journey we have chosen to go on by being animal lovers. I think we need to remember these chickens have been at this alot longer than we have, she is focused on the 2 healthy ones. go and enjoy them.
I took your advice and I put her egg back down with her and the other babies. If it hatches it hatches. I did keep it pretty warm in my bra though LOL!!!