Looking at the geography, but without any local knowledge, I don't know why it is sometimes assumed that Ruth either went up Boxhill or wanted to give the impression that she had done so. Why would anyone think that just from the fact that the hill was nearby? There was a big pub, shops and houses. It isn't a natural conclusion when someone is dropped off there late in the day in winter. Of course, the letters were found later, but they could have been put there before or after and could be the work of an accomplice.
Did she specify a drop off by a pathway that leads to the hill? Or did she ask for the pub?