Naked or not, girlfriend or not, scrubbing the gravel out hurts like holy hell and took well over an hour to complete. She scrubbed and rinsed. Scrub some more and rinse. Repeat until no more foreign mater was present. She did it very well, and very thoroughly. I mostly just grit my teeth and hung on. After that I was exhausted and slept for over twelve hours.
Having it done after a long soak, and fortified with a stiff drink seemed to dull the pain and allow it to go faster.
Now don't get me wrong, the naked girlfriend aspect tends to be comforting but the pain tends to ruin the mood. As much as I would like to think seeing me prone generally inspires women everywhere to remove their clothing the real reason she stripped was to keep her clothes from getting stained with blood. The straddling part made it possible for a 100 pound woman to hold me down while she held the limb with one hand and scrubbed with the other.
Sitting on a person your treating helps to control the situation and limits wiggling and flinching. Standard practice when treating livestock. If you ever have to provide first-aid to someone while your in a vehicle moving over rough ground, or vessel on rough seas, sitting on them stabilizes your movement to theirs and allows some level of delicacy and precision even as everything around you bucks and heaves.