It could be she has learned this behavior has she recently made new friends at school, or near her home, there is a lot of peer pressure and children copy friends they admire . I would say if you do not use 'bad language then someone else is, has she any new babysitter/older family members,would also account for her rebellious behavior, it is possible some hormones are involved aswell.Ask her friends round to the house for a 'play date' then keep your eyes open /listen in to the conversation, all may be well but if you are a hands on Mom and you sound as if you are ,you will realise that being involved is the way to go ,you will have more of this to contend with in the future trust me this is a learning curve....