When you feel disappointed, you are feeling deprived of something you thought was already in motion. If you're feeling like you have an "appointment" with a promotion or a successful presentation or a new love, having that thing not work out is especially crushing because it was kind of a done deal inside your mind.
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.