Is there any possibility of you getting a few more pullets around her age? Even one would really help, or two or three if they're a little younger/ smaller than her. Sadly, integrating just one chick is very difficult, especially as Mama has already abandoned her. Any friends her own age, or closer to it, would ease the stress of integration (but only of you had very thoroughly integrated her and the new ones beforehand!). If you can't get any more chicks, then I think you just have to be very patient. Get a dog crate or something in the coop that will allow her and your flock to see but not touch. If you have a big run, hang out with her inside of it, and let her interact with the rest of your flock where she still has room to run away. Eventually leave the door of the crate open just enough for her to get in, but not the full grown hens/ rooster. Be prepared for the fact that she may never really become part of the flock- ideally, they won't pick on her to the point of energy, but she may always end up being a little lonely.
I'd recommend waiting to start integrating for another week or two, just so she can feather out and bulk up a little more. How much are you home during the day to spend time with her?
The other option would be to see about rehoming her- there might be someone on craigslist looking for a single pet/ house chicken, or a companion for a lone pullet of their own. It sucks to hear it, but she really would be happier with a friend her own age.
Good luck with whatever you decide to do. I'm interested to hear what others suggest.