Cats sleep a lot during the day and come out at night, that's when she will go exploring. If possible maybe mom can stay up and put out a plate of canned food, that will get the kitty moving. Then she might be able to speak to the cat so she will get used to her voice and start building trust. Cats won't eat what they can't smell so the stinkier the food the better. Also, look up, cats like to climb. When I adopted my cat he somehow was able to get on top on my kitchen cabinets and hid in the space between the top of the cabinets and the ceiling.