Cat Hiding please help

Back in October 2003 we adopted a torishel cat, Female, 3 years old.
From Oct until Jan 2005 she hid in our recroom in the cubby hole
underneath our mainfloor bathroom. (basically where the ceiling and
wall meet) By a fluke we managed to get her out of there. She came
upstairs to eat and we closed the door to the furnace room where she
had been hiding.

its been 2 weeks and now she constantly hides underneath our spare room
bed. She doesnt come out on her own except to eat and use the litter.
If we try to make contact with her she will run underneath our spare
room dresser. She clearly doesnt want to have any affection or
socialization. We have 1 other cat and he doesnt bug her and the 2 of
them never fight. She just sits underneath the bed all day.

There was an ad in the paper for her and we adopted her. I know it
takes some time for cats to adjust to thier new environment cause I
have adopted many before this, but I have never known a cat to take
almost 4 months to come out from hiding. I am just frusterated that
she wants to be left alone. Any ideas on what I can do?