My children are 1.5 years apart (closer I suspect than these siblings in age). Both are boys. My oldest has far more responsibility because of his size, ability to communicate and ability to reason to control the situation than his 2 year old brother. He always has the ability to walk away and tell me what is happening. Perhaps the father felt the same way about his eldest and that's why he posed the question the way he did. Nothing to do with her being a girl, but because the oldest has the ability to take on more responsibility. 

And in case someone thinks it's unfair to place a larger burden on the oldest, they also have later bed times, freedom to grab their own snacks etc.. The youngest will have all the responsibilities and privileges my oldest enjoys as he reaches the same age/abilities. This is natural.

The oldest could walk away and tell a parent what is happening rather than become a victim. They have the size and cognitive ability to do so. And they should. Boy or Girl.