How to fish low voltage wire from finished attic dormer through heavy framing?
It's probably reasonable to assume the wall board has equal thickness above the ledge and below the ledge. Then you can measure the depth of the ledge at the yellow arrow, which is front-face to front-face of the wall board. Bring that measurement into the crawl space and measure off the back side of the lower wall -- this tells you where the back side of the upper wall is at. Add another inch and you've got a position that is comfortably inside the upper part of the wall.
If you'll still prefer to drill down rather than up, consider a long drill bit (sometimes called a bellhanger drill bit). You could use it to pierce the interior drywall and continue on through the lower framing. Yet another approach is to remove the right-hand piece of window casing. There should be a gap between the window and the rough opening. You can drill down in that space, again with the bellhanger bit, and afterward reinstall or replace the wood casing instead of repairing a hole in the wall.