Is This Unusual?

If she's been bleeding for over a week, she definitely needs to see a doctor, whether she approves of it or not.  At 12 years of age, she is not old enough to realize that there may be something wrong with her that needs medical attention immediately.  A period that lasts that long could lead to anemia, or she may be hemorraging to a degree.

Just to be safe I would take her to the gynecologist, besides now that she is a young woman she should have a gyno.

First of all, has she shared whether or not it is a light spotting or full heavy bleeding, those are somethings to consider, also, you should sit down and explain what will happen at the doctors office, if she is seen, there is a fear of the unknown, especially in 12 year olds, I know Mine have never been regular, so I tend to spot off and on and yes sometimes for 2 weeks. If you feel uncomfortable talking with her, there is always the school nurse, who may be able to help or an aunt, Just keep in mind as well, even at 40+ we don't enjoy having it done either.