My Cat Won't Enter Half the House

I have an adopted female 3 year old cat, Mandy, that I have owned since Jan.. 1st of 2012. She reportedly was an outdoor, feral cat (her ear is notched) but is very socialized to people - very sweet. They told me she would be shy to explore the house and to let her take her time. So it has been 8 months and she basically stays in half my main floor of the house - my computer room which has my cat platforms and the cat food, my bedroom which is the adjoining room and the bathroom where the litter box resides. She has made the rare pass through the living room but pretty much never goes in the living room, dining room or kitchen. I also have a nice sun porch she could enjoy with views of the yard.

I guess life can go on this way, but I think it would be nice if she felt comfortable in the rest of the house. She seems happy enough so maybe it's all a problem for me only. I was wondering what others think. Should I do nothing or is there something I can do to help her widen her horizons? What would you suggest? I hesitate to carry her into the other rooms because she gets fearful. I have tried calling to her which has gotten her as far as the entry to the kitchen. By the way, after I had her 2 months, I adopted a second female cat (1 year old). Mandy is friends with the other cat (Flag). Flag is a confident cat and is into everything in the house, but this example hasn't helped Mandy.

Thanks for your thoughts.