Child Using Foul Language
Curbing the Urge
In terms of disciplining the new and troubling behavior, if your child receives an allowance, consider docking it fifty cents every time she uses a swear word. This method is effective with children who are motivated by money. If money isn't her motivator, take away other things incrementally instead: Limit the time she can be on the computer, cut back on her phone use, roll up her bedtime, etc. She'll eventually get the message.
As children negotiate the developmental years they push for more control over their own lives. You are at a crucial time in your growing child's life and you need to find ways to positively support her need for independence. By doing this -- and not trying to control every little thing she does -- you will encourage her to develop into a capable, competent person.
So let her choose her clothes (within reason), let her pick hairstyles, and her extracurricular activities (maybe she wants to be a soccer goalie, not a ballerina). Give her free reign to decorate her room to her tastes, and don't try to control how she spends her allowance. Begin allowing her to venture out on some safe excursions with her friends to the local park or mall without adult supervision.
By encouraging positively empowering behaviors in your daughter, your foul-mouthed little tyrant may blossom into a confident, savvy and capable teen -- even when she is at home.