Socialising our semi-feral cat update:
had to kick her out of the spare room over the weekend, which was fairly eventful as she refused to be shepherded towards the area we'd setup for her (sheltered corner of the front room), running first into the basement, then deciding to reside on the kitchen window sill after being in the front room for a few hours. The latter was really bad, as the kitchen is small, and we were freaking her out by getting too close whenever we needed to cook or otherwise use the kitchen, and we couldn't shift her as she was pretty wedged in and refusing to move, with a few hisses etc thrown in (first time I've been hissed at ). Eventually she moved back out (I think she figured out it wasn't a good spot, and left when we left the house for a while in the hope that she would move) and under the sofa in the front room, where she's been for the last day and a half, very slowly getting her appetite back, and generally chilling out a lot more.
Hopefully being a bit more exposed to us without us actually paying attention to her (eg whilst watching TV, playing games etc) will help further. She has a pretty sheltered spot under the sofa (has a material fringe that goes almost to the floor).