Am I at fault for saying "shame on you" to a child to stop her from repeating a word I don't want to hear from her?

Reprimanding your niece for using obscene words is a religious obligation, as it falls under the category of enjoining what is right and forbidding what is wrong; because vile language, which causes shame, is forbidden by Islamic law. Prophetic traditions have indicated Allah's abhorrence of the vulgar and obscene. Abu Al-Darda reported that the Prophet, peace and blessings be upon him, said: "Nothing is heavier in the believer's balance on the Day of Resurrection than good character, and indeed Allah detests the vulgar and obscene." And also his saying, peace and blessings be upon him: "The believer is not a slanderer, nor a curser, nor an obscenity, nor a foul-mouthed person."