My cat is always scared and hiding?

We've had her since kittenhood and she has always been scared and hides behind furniture. We have 3 dogs and 3 other cats that she snuggles with elsewhere, always hiding. She never asks for a pet and hates to be held! People come over and swear she doesn't exist! I love her and I don't want to get rid of her but inside my heart I think she would be better as an only cat in someone else's home. What should I do?