Slander on the job, is this defamation of character?

my boss had a meeting with her office workers, myself included. She said that she wanted a fulltimer who is honest and reliable to work sundays. i am parttime and i am the only one who works sundays. I asked my boss to repeat the remark she made,she said it again. I said are you referring to me? and she said actually yes i am. I have never called in on a sunday sick. She said she heard i we as leaving early and not telling anybody from the istant manager. We had a meeting with myself my boss and the istant manager. The istant manger said she never said such a thing to my boss. She said that she needed somenone to stay later in the day because the time i get off is too early. Is this defamation of character by my boss and can i do something about it. She did apologize but she defamed my in front of my coworkers and other people in the office.