Good. You're doing a very good job and your patience is just wonderful. You have excellent instincts and I encourage you to follow them.
She's going to surprise you one day or night and it'll make all the difference in the world. One of my most skittish and poorly treated rescued cats was a master at hiding. I couldn't find him anywhere for just about the same amount of time as you've had your girl. I knew he was still with me because the food and water would need replacing every day, and the litter box was regularly used. Now and then I'd see a darting shadow out of the corner of my eye.
One night while sitting in bed watching something on t.v. - this "ghost cat" appeared at the doorway, hesitated just a moment and then jumped into bed. He decided that enough was enough and I must be ok.
He's the oldest resident in my rescue, just short of 20 years old now. He wasn't quite a year old when I rescued him.
So you just keep doing what you're doing and stay patient.
Another option that might be helpful is a product called "Feliway".
- it's a plug in, like an air freshener, but of pheromones that humans can't detect/smell.
It helps calm the cats.
It's important to continue through at least 3 refills (each refill lasts about 3 months) - and be very sure you don't let the device go dry between refills.
It can be supplemented with a room spray, but the room spray won't work by itself since the animal needs more long-term exposure to it.
It's available in PetSmart and other stores, plus of course online.
To make sure you're giving her the best nutritional options, take a look here www.catinfo.org for some terrific insights by a vet specializing in feline nutrition (and even providing homemade recipes for your cat).
Please keep me informed through this ok? I look forward to hearing when she decides she's going to keep you and begins sharing her own affection freely.