If you Google
"Oxford Road" "Upper Richmond Road" Putney
you get a Google maps result, with the red pindrop pretty much right on the PoW. If you go to Streetview at that point, and move into Oxford Road then face right, you can see the PoW has seven windows onto Oxford Road. From left to right, I'll think of these as windows 1 to 7 for convenience. The pavement hatch for barrel deliveries is under window 6. The cellar, as I understand DV, runs right to left, from windows 3 to 7. The steps down into the cellar are fore and aft as we look at the pavement hatch, I think. The two leftmost windows, 1 and 2, are the dining area, under whose floor DV thinks SJL is. At cellar level, there's a wall between windows 2 and 3, parallel to Upper Richmond Road, which is pierced by the hatch he looked through and saw the mound of rubbish.
The exterior door furthest left opens into a lean-to outbuilding. You can see this best in Google Earth view. It's about half the depth of the dining area, and there's a small yard behind it that takes up the north-east corner of the PoW's plot. I would guess this is the bin store, and that staff can access it from the yard and would take the bins out through the street door.
It's not possible to see what separates the PoW's yard from the embankment. I have to say, though, that as great an undisturbed hiding place as this embankment is, it doesn't look easy to get a body onto it, if it's under that floor to begin with. Unless there is access to that underfloor void from the lean-to store, to get SJL's body onto the embankment you'd have to bring her back out through the hatch; carry her up the cellar steps to the ground floor of the pub; and carry her through the pub and presumably its kitchen to get out into that yard. You've then got to get yourself, SJL and maybe a shovel over the boundary - whatever was there; chain link fence? - and then you're on the embankment. This requires free run of the pub when nobody's around.
It's possible, but a far simpler way if you have a vehicle would be to first move her from the void to the bottom of the beer hatch at about 4 or 5AM. You then go up and park alongside the pavement hatch. You then lift her up through the hatchway and into your vehicle. Quick, almost unobservable, and unremarkable because if anyone sees you it'll look like a beer delivery is expected. You dump her somewhere and by 6AM you're back in bed.
If that is what happened, this is not going to get solved.