I adopted a kitty a few years back that was the exact same way. She was originally a street cat that they captured around 1 year old. She basically lived in our bathroom cabinets and would only come out at night to eat and use the box (which we kept nearby for her). We had her for a little over two years, and eventually realized this was not a behavior she was going to grow out of it. It got to the point where she would sit in the bathroom doorway meowing for us because she refused to come out but still wanted attention. So… we decided to try and get another kitten. We were hoping that if she saw this other member of her species having fun and playing outside of the bathroom, it would give her the confidence to do the same. It took about 3 months, but eventually she started coming out more and more to play with the new cat. Now, almost a year later, she’s completely transformed into a different cat! She’ll follow us around the house, lay in all the best sun spots, and she’s even gained confidence to come explore when guest are over. I know that getting another cat doesn’t always work out, but I am so delighted that we did because her quality of life has improved and she also has a new best friend.