Regarding your cat - sorry, I don't know what to think about your chickens - If she has kittens you would be able to see her nipples and the hair around them would be worn off, so they would be pretty easy to see. And, this is how you tell when they get close to having kittens . . they get full of milk, although not as apparent as when nursing. Although if she is fat, she hasn't had them. She'll be skinny right afterwards.
Momma kitties are totally sneaky about birth, whether in the house or outside. Outside cats will hide them as much as they can (because of Toms and other predators). In walls of barns or sheds, under bales of hay or straw, in the ceiling . . it's amazing. Then, if you can't get to the kittens they grow up wild. You definitely don't want that. Maybe you could start giving her a treat, like milk or tuna, each day at the same time so she starts coming around same time every day. Just an idea.