I’ve done a small experiment:
Take a pen. Now if you imagine that you’re the one …handling it (the palm of your hand faces down). With my hand it takes one fist + 3 fingers (from pinkie and up). Now if i hold it with palms facing up, i need both fists entirely.
The above can be imagined that your girlfriend is staring eyes to one eye (dry land) and looking you in the eyes (in water) so i think the technique of handling it is different.
I think it’s because of the pointer finger. It more comfortable to angle or ‘snuggle’ the pointer finger and thumb against something (palm up) not so with the pinkie.
