I do trap and dispose, but I gotta say: you will never be able trap all of the predators that are interested in unprotected chickens. Spend your money, time and effort fortifying their coop so the hens have a safe place to roost at night. As long as there is an easy meal you will see a steady...
Any chance she could have been bitten? Even a small puncture wound from dogs or cats can be very harmful to smaller animals due to the bacteria in their mouths.