Baby chick dead... only the head found !!!! ???

Doing research I found where chickens / chicks were found dead without their heads, but this morning I went out to the coop and found a baby chicks head nothing else no feathers or other parts that I could see. This was a chick with no mother earlier I found the mother dead and her 3 chicks were by her side.I do not know if another hen killed her.
Would another mother kill and eat another chick and only leave its head????I was so mad I threw the mother out of the pen for the safety of the other chicks.After doing some research I thought maybe I was wrong ?
I had separated the orphan chicks but sometimes a chick sneaks over to the other side through the fence and the mother just flies over to top to be with it... like this morning and when I went to put them back on their own side and noticed a baby chick was missing... then I found its head! It was horrible.What do you think happened? Now I am sad for the mother that I threw out she keeps trying to get back in,I do not know what to do. Thanks Vickilynn