This is so sad, I am so sorry for you. Predators can squeeze through incredibly small openings anyway, and you won't like hearing this, but "chicken wire" is ONLY good for separating chickens from each other, it does not have the strength or small enough openings to keep out a determined predator. Which is what you have. The good news if you can call it that is it's attacking only at night, right? So you have until tonight to protect your other two hens and figure this out. You may need to make some tempory arrangements to keep them safe, while you work at turning your coop into Fort Knox. I'd suggest start with their roosting area and go over it closely. ANY hole bigger than an half inch you'll need to plug with something strong. 1/2" hardware cloth, the sturdy wire mesh, is really the only way to go on the coop. The window by their roost for example, a weasel, snake, a rat, a dozens things maybe could get through there. They need air, ventilation yes, but that is at least one spot that popped out to me as an possible entry point Look at the roof, floor, use a flashlight and someone on the other side to look for holes you didn't know we're there.
Do you have any other chicken people around that can keep your hens for a couple days, until you get this taken care of?
Good luck, I'm sure you'll figure it out.