i had the same bug. I find that after about 3-4 hours of play from a new game sally randomly finds me in the dc wastes, first it was the superduper mart and next time was at gnr radio building.anyhow, she finds me and says the old 'hey are you escaping too? i can be real usful blah blah". This is oviously a bad bug. to try and get around this bug, i tried loading a slightly earlyer save before she shows up in the waste and from there go to straight to zeta, but then, inside zeta, as you described, sally is no where around :( at the moment im trying earlier saves to see if i can find the point that it buggered up for me this time round, but the first time, i found the way to fix was to make zeta the first thing that you do on a new game, get it out the way then then on in it should be fine...touchwood...