Any way the movie was about a young girl who came from a very spiritual family. She was a good christian. But after going to college she started to experience things, that were very demon like. After a while she started having convulsions and blackouts and symptoms very much like psycosis. Anyway to cut the story in half she is possesed, and dies after a exorcism done by her priest.
I have not seen the movie, but by your discription, it seems to have some discrepancies in lining up with scriptures.
1John 4:4
But you belong to God, my dear children. You have already won your fight with these false prophets, because the Spirit who lives in you is greater than the spirit who lives in the world.
If we are in a right relationship with Christ, there is no demon or even satan himself that can possess (enter)us. Satan can howerever tempt us and lead us away from our obedience to Christ. When we are led by the Spirit of God we are the sons of God. But if we walk after the flesh we become a play ground for demons.
Galations 5:16-26
16*So I advise you to live according to your new life in the Holy Spirit. Then you won’t be doing what your sinful nature craves. 17*The old sinful nature loves to do evil, which is just opposite from what the Holy Spirit wants. And the Spirit gives us desires that are opposite from what the sinful nature desires. These two forces are constantly fighting each other, and your choices are never free from this conflict. 18*But when you are directed by the Holy Spirit, you are no longer subject to the law.
19*When you follow the desires of your sinful nature, your lives will produce these evil results: sexual immorality, impure thoughts, eagerness for lustful pleasure, 20 idolatry, participation in demonic activities, hostility, quarreling, jealousy, outbursts of anger, selfish ambition, divisions, the feeling that everyone is wrong except those in your own little group, 21*envy, drunkenness, wild parties, and other kinds of sin. Let me tell you again, as I have before, that anyone living that sort of life will not inherit the Kingdom of God.
22*But when the Holy Spirit controls our lives, he will produce this kind of fruit in us: love, joy, peace, patience, kindness, goodness, faithfulness, 23*gentleness, and self-control. Here there is no conflict with the law.
24*Those who belong to Christ Jesus have nailed the passions and desires of their sinful nature to his cross and crucified them there. 25*If we are living now by the Holy Spirit, let us follow the Holy Spirit’s leading in every part of our lives. 26*Let us not become conceited, or irritate one another, or be jealous of one another.
If we succumb to the enemy (the flesh) and become harrassed, oppressed by a demonic spirit. All we need to do is obey Christ to gain deliverance from the demonic force.
James 4:7
Submit yourselves therefore to God. Resist the devil, and he will flee from you.
As far as the exorcism methods of the catholic church, plain and simple religious mumbo jumbo. The power to cast out devils is not in holy water, oil or a gold cross. It is however in every believer and is by the name Jesus the Christ and His authority.
Mark 16:15-18
15*And he said unto them, Go ye into all the world, and preach the gospel to every creature. 16*He that believeth and is baptized shall be saved; but he that believeth not shall be damned. 17*
And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues; 18*they shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover.
Satan's goal is to distract us from keeping our eyes on Jesus. He will pretend to be an angel of light, a lady in a red dress and high heels, a night in shinning armor , the harmless little tooth fairy or even the boogieman. As long as he is a distraction, he is happy. Yes we should be aware that he is out there, but as long as we focus on Christ and remain submitted to Him, satan is kept
"out there".