Why won t my rat come out of the tunnel? And how do I get her out?

She is most likely still afraid, which is completely understandable since you just got her last night. Give her a few days to get used to her new set up. Once a few days have passed, try holding treats in your hands and let her come to you. Don't make sudden movements, or else she will be even more freaked out. It just takes a little time and patience :) Another thing, I would get her a companion. Rats are very social creatures and if she has a friend, that will most likely get rid of some of her shyness.

put food near the entrance he'll come out when he gets hungry

She's in a new place and is scared just give her time.

Maybe she's scared shitless?