It looks to me to be about level with the bottom of the windows in the vehicle up ahead, so 3 feet high at least.
In terms of hoisting her body up to and over the top, I can't decide whether rigor mortis would make that easier or harder.
One rule of thumb is 12-12-12, ie 12 hours to set in fully, 12 hours in full, rigor and then 12 hours for it to gradually resolve.
If she did die on the way down to Memphis it's difficult to know whether rigor would be active or not by the time he got to the bridge. Its onset and passing tends to be quicker in violent deaths than in natural causes ones, and slower in low temperatures.