First off, I am sorry for the loss of your girl. I have not dealt with martens, but I have some experience with their "cousin," the mink -- who also seem to kill for sport not for consumption of the bird.
Minks will always come back and try again, and they are able to squeeze through the smallest openings, where it seems impossible.
I don't know what your coop is made of, but 1/2-inch hardware cloth is your best friend. Fasten it over any gaps or holes. Don't just staple it in, really fasten that stuff down. I lay the hardware cloth down, then lay 1-by-2's on top of it and screw those down.