A happy baby is a baby who knows there are rules. This is one of the great ironies of becoming a parent and it takes a while to figure out: Although babies bring chaos into your life, they don't actually like chaos. Even though they make a huge mess, they actually prefer a nice tidy world, one in which they can depend on simple routines and reliable outcomes.
Teenage girls are sensitive to the way people in authority talk to them, especially their mothers. They are easily wounded, feel criticized, and vulnerable when they sense or get outright disapproval. However, mothers are only trying to shape them up to be young women and don't understand their sensitive narcissism.