Lily, a new feral cat in my life

I have fostered stray cats before, but only kittens. Currently I am living with a new cat who has had a few litters before and is newly spayed. Her name is Lily and is just like her daughter, Annie, that I fostered 3 months ago. She is all black and is very sweet. She has not hissed or scratched at me once.
I understand that feral cats are scared at first, but I have had Lily for a week now and I'm getting discouraged. She hides around my apartment all day.
The good thing about Lily is that she is very clean. She only goes to the bathroom in her cage which i line with newspaper. I recently introduced her litterbox into her cage and i saw just today that she went in the litterbox! I was really excited that she learned so quick.
I am working everyday at winning her trust. I really wish she would come out of hiding soon.
I just joined thecatsite.com because she is the most difficult cat I have had and I need support from other feral cat owners.

From what I have seen some ferals take longer.
A friend of mine only takes care of ferals and she has 5 at home now. It took months of hard work but they are bonded for life to her and her children. One of them gets bullied and has a need to hunt so she lets her out. She also has 15 acres of land in a rural setting.

What I saw her do is just be very very patient. Sooner or later she will come around.
Her hardest cat now stands on her shoulders as she gardens and does work around her land.