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

I think, you should ask her what did it mean what she said and where she heard it. Be calm, more anger you will show more stubborn she will become. Talk to her and ask her does momma talk to you like this? Does momma use such words? Don't I talk nicely to use? And if she again uses such word, do not talk to her and make her realise that it is not okay to use the word. Since, she is 9, you can ignore this thing.