Ruth started out modelling for me, then assisting and modelling. Now she models, assists and shoots as well. Does all of them really, really well. Still can't organise the gear cupboard or make coffee the right colour, but ho hum, she's forgiven.
Girls make great assistants cause they do the job - they assist. They don't zone out and think how they'd do the shoot if they were boss, but most of all they don't hit on the models, they just pay attention and make it a bit easier for everyone to get through the day.
Girls make great photographers because other girls - the models - don't try to do that smiley chatty thing that makes all boys brains melt to the point they stop shooting and monologue about how great they are. (shooters out there - you think they really care what us old people think about ANYTHING? LOL)
Girls shooting girls doesn't always work, some girls hate it and go all shy, others thrive on it and there's no real way to tell before the shoot.