Need help with a feral kitten I'm fostering.

So, we're having Thanksgiving dinner and I look out on the patio and there's this white, long-hair furball, maybe about 7 or 8 weeks old, GORGING herself on my outside cats' cat food. This tells me she's starving. I tried to go out to the patio to ascertain if she was wild or not, she is. Since I can't bring her in without trapping her (something I never do unless there's a medical emergency) but I'm watching her in the back yard for a couple of days and notice she's made friends with one of my 6 cats -- Erica. At one point, Erica sort of goes and gets her and leads her to the sliding glass door which leads into our family room. I opened the door and in she comes. I closed the door and have had her in ever since.

After 2 or 3 days she sees we're not going to reach for her or try to coerce her so she's comfortable sleeping on the futon and the chair and the table and on my desk -- out in the open. She's still following Erica around like they are Besties. Erica is tolerating her, even bathing her, but Alaska (we named her) is FULL of fleas and too young to treat yet (she's getting there) so it's understandable that Erica is not wanting to be too close to her.

ANYWAY . . . anytime I try to come up to her, including on her level, and very gently, she dives under something. I've been able to pick her up a few times but only when she was unsuspecting and she doesn't seem to want to stay in my lap even though she purrs loudly when I actually get her there.

I know her instinct is to dive under something when she's afraid but I need to be able to touch her at will so she doesn't freak out every time. As I said, I'm FOSTERING her (I already have 6 cats) and it's important that she be able to be handled in order to be adoptable.

I'm taking her to the vet on Tuesday to get her shots, an estimate of how old she is and maybe get her de-flead if she's old enough. I'll get her spayed as soon as it's medically possible.

This is my question: How do I get her to allow me to pet her/touch her/hold her without her freaking out?

Btw, she's solid white except for a black "skid mark" on her head and she's got one green eye and one blue eye. Cutest damned thing I ever saw.