I think refs totally under-card female players, I've seen more cards handed out for relatively minor stuff in one season of U12 boys soccer than I've seen in a decade of girls/women's soccer with much worse fouls.
I won't comment on that comparison specifically (too little data), but I was proud of my co-coach on a U12 team. In a middle-school game Aaron threw down an opponent away from the ball. The ref missed it, but I didn't and yelled at Aaron that he was better than that (he flipped me off). His coach (also his father and my co-coach) didn't miss it either - he immediately yanked his son for 15 minutes (the red card penalty in local middle school soccer is 10 minutes). He didn't
quite go the whole route (he subbed in a player, whereas a red card means playing down a player), but since Aaron was by far the best player on the field, a sub hardly mattered.

It ended up costing them the game (my son's team scored 3 goals while Aaron was out), but
may make Aaron a better player and person. (His father and I agree that he is usually the best player AND the most likely to be thrown out for most games.)