Has my 12-year old lost her mind?

She's SOOO moody, sarcastic, and disrespectful. She's always been a model child and sometimes it's hard to recognize her. Is it hormones? How can I tell if there is something really wrong or if it's puberty> She won't talk to me about anything. Just wants to be left alone. This was not in the brochure when I decided to have a baby!!