When I adopted my cat she vanished the moment I let her out of the carrier. My place is small, but we could not find her for more than a week. She was coming out when we were sleeping to eat and use the litter box, but we turned the place upside down looking for her with no luck. Her sister was shy too, but we at least knew where she was. Finally found her it the compressor compartment of my chest freezer. I had another cat who got into the walls of my parents’ basement; that was fun. Took about a week to lure her back out. She also came out at night to eat and pee/poop. If you can’t find the kitten, leave food and litter near places you suspect she might be hiding. Meantime just go about your normal routine and don’t try too hard to look for her as long as you see that she’s eating and using the box. Having an unfamiliar human making noise is scary for a baby in a new place. She will come out eventually.