What is the title of this movie?!!!

[Julia]

OK so there is this movie that I watched a while ago and I can not, for the life of me, figure out the title to watch it again.

The movie is about a little girl (we'll call her girl A) who can see ghosts. She befriends girl B, a girl at her school. Girl B's sister had supposedly died of something (nt sure about this detail) but her ghost proves otherwise, it was the dead sister and her sister, girl B's father who killed her. Girl A sees that Girl B's sister goes into the body of Girl B. While in girl b, she attempts several murders including that of girl A. Somewhere in the storyline, something is stolen from the teacher, like a pin or something of importance. Also, at the end, girl B (who will not leave girl A alone) attempts to kill girl A and the teacher. Girl A is locked in a shed and the shed is set on fire, but she gets out. At the very end, the girls and the teacher are in a forest and girl B (with her sister's ghost inside her) threatens to kill girl A with a knife. (it is night and in a forest) Girl A tries to convince girl B that she is not bad and tries to tell her that it is her sister. But instead, the girl B turns and stabs the teacher. I do nto think that she (the teacher) dies though. I think that girl B dies at the end. 

I really want to watch this movie so THANK YOU!! it is driving me crazy!!

[Julia]

http://www.imdb.com/title/tt0884227/ Thank you, Zombie Jones! but I figured it out recently; it is a movie called Within.