I would say don't go to the doctors yet, It may be the age as she is growing up and testing the boundaries with adults.
Ask round see if her friends are mouthy, she maybe getting from them.
I have friends with teenagers who are mouthy and getting into trouble and My little girl is 8 and gets mouthy at times as she goes to Junior school now and isn't a little girl anymore. At times i feel I have an 18 yr old!!
So your not alone it will get better