"The girl takes her jacket off."
Translation:La fille enlève sa veste.
It's not reflexive because the verb is acting on the jacket. What is being removed? Sa veste. This is different from dressing or undressing (oneself). Elle s'habille or she is dressing (herself). What is being dressed? Elle, the girl or the woman. Note that there isn't another person or thing listed after the verb; the verb habiller is acting on the subject. It's the same thing for undressing or getting undressed, elle se déhabille. She is getting (herself) undressed.