Why do people say I'm doing my job when a student says "I hate you!"? I'm an assistant teacher and punished her (please read)?

Today I punished a student for taking back to me and saying nasty things to me. She though I was joking and didn't listen to me. I told her I wasn't kidding. Then she said, "I hate you! You're a mean teacher!" I put her in time out at recess. I'm hurt. The teacher said, "That means you're doing your job. You're not here ti be the students friend. Be their teacher and do their job. Who cares of some don't like you?" One of the students called her a mean teacher. She smiled and said, "I don't mind being called that." And talked away. She is a TOUGHIE.