Welcome to TCS and thank you for rescuing this kitty!!!!
How old your feral is will affect the amount of time it takes for her to trust. Her background with people will also affect the amount of time it takes for her to trust. If people threw things at her, kicked her, squirted things at her - whatever - that is affecting her.
The most important thing in building trust is time, plain and simple. For an older feral (meaning a feral that was rescued that was older than maybe 4 months), six months is not a long time.
I don't know what things you've done to help her learn that you want nothing from her, but that is the first and most important lesson. Don't reach after her, don't chase after her, don't force anything. Just being around - ignoring her - is really the best thing to do.
After that, knowing that cats learn by association can really help. Helping her to associate you with good things can help turn the corner. If you haven't already, get a t-shirt really sweaty. Leave treats out on it for her. Get another t-shirt really sweaty - leave it under her food dish.
As to a pal? It is so hard to know in advance how the resident kitty is going to respond. We now know that Lazlo (our first rescue) would have been perfectly happy to be an only cat. He's a good big brother to the rest of the crew, and bringing in new kitties wasn't too traumatic for him. But for our Spooky, it takes her at least six months to adjust to new additions. She hisses, spits, bats at new kitties.
If you want another kitty to have and to cuddle (remember - there are NO guarantees that any kitty is going to be cuddly!), it would be best to get a neutered male that is younger than your current kitty.
DO keep them separated for some time - there's no actual rule, but a few days to a month. It depends upon the reaction of your feral girl. Again - let her get used to the idea that she'll be sharing her territory. Swap smells - rub new kitty with a towel, and put treats out on it for her. Do the same thing with her for him. Get a catnip toy - if he's a young kitten, the "catnip" thing may not be activated yet - but if it is, he'll rub and drool all over it. Then give it to her to play with. (Remember - don't leave catnip toys out, the kitties get "immune" to them. Pick them up at the next morning, and don't put them out again for a week or so). Again, do this with her for him.
Getting them to associate each other's smells with good things will help smooth the actual meeting. And if her hidey places are in your bedroom, unfortunately that will not be a good room to separate him in.
We had to keep Ming Loy in a separate room when we brought her home. It broke our hearts not to have her in our bedroom, but it was everyone's safe space. We'd wake up in the middle of the night and go to check on her. She was always sleeping squeezed underneath a blanket chest we had in there, and it would take her a few minutes to wiggle out. So we'd open the door and say "Where's Ming Loy?" Turns out - she came to answer to "Where's Ming Loy?" and not "Ming Loy."
For a while there she thought her name was "Where's Ming Loy." Silly little girl.
BTW - we ended up leaving the door open and putting up a child gate. Our other ferals were scared enough they didn't jump into the room. That worked for two days until she figured out she could climb over it. So we put one on top of the other, and that worked. And it let them smell each other and get used to seeing each other before we let her out. Some people go so far as to put up a screen door. That works really well if you're willing to do it.
Here are a few links you may find helpful:
On introducing a new kitty:http://www.thecatsite.com/Behavior/4...cing-Cats.html
...and remember - we're here for any questions along the way.