In the movie, the priest tells how Emily had a vision of Mary (Jesus' mom, not the other one) and Mary told her she could either come and stop suffering or stay and her story would be told to the world and they'd know the Lord. So Emily stayed because she felt that whatever happened to her it was her mission to spread the word of the Lord.
So everyone who thought the movie pimped the devil; "Oh snap! I was wrong!".
Like I said, it was a very good movie.
If you aren't secure in your faith, then you should probably refrain from a lot of activities. Not just movies, but going to the beach where scantily clad females gather. Or walking through some malls where various shops are pumping out secular music. The point is that you're either saved or you're not, and you can't protect yourself no matter how deep your faith from the assaults of the enemy.
The best thing I ever heard, and it's so true, is that if you look around you and everything in your life is wonderful... Well, you know what that's a sign of, don't you.
I also like how some people absolutely refuse to believe their's a devil. That's cracks me up to no end that someone thinks that by closing their mind to it it will go away. I can confirm that this technique only works with physical pain, and even then it has limits.
In short, go see the movie (er, rent it I mean, fye on Hollywood!) if you think you would like a good drama that has some spiritual imagery and theme. Well, only if you are secure in your salvation and faith I guess...