Time passed, and a few weeks ago we noticed she was getting a little podgy, then most definitely pregnant, and now she has had the kittens. She is still in the bramble bushes, and none of the houses around about seem to know of anyone who has had a tabby cat go missing. But none of them were even aware of her existence (sad state of affairs, but that's a rant for another day!)
So now, we have a daily ritual of going to feed her. She still has milk, so we are hoping the kittens are doing ok, in the depths of the bramble bushes.
She is so friendly.