My 9 year old daughter swore at me today.What do I do to stop her from talking like this?

first ask her where she heard it and tell her it's not a nice word and is in fact a rude word. tell her that it is something that is definitely unacceptable and will come with serious consequences in terms of behavioral punishment. tell her that you know her very well and know that she is a smart girl, who will not use words that are wrong and that you know she will not disappoint you. once you show her how much confidence you have in her, she will try to live up to it. also, kids at this age pick up a lot of things from media and people at home, so it's possible one of her friends said it. tell her to ignore this in future and not repeat.