My sister is possessed, what do I do?

Lock her in a room with a Bible-story coloring book and some crayons for a few hours. Always works for me.

God is not mocked ...

Gal. 6:7 Do not be deceived, God is not mocked; for whatever a man sows, that he will also reap.

Prov. 14:6-7

6 A scoffer seeks wisdom and does not find it,

But knowledge is easy to him who understands.

7 Go from the presence of a foolish man,

When you do not perceive in him the lips of knowledge.

Eventhough this is probably not happening, Im still going to reply. Who the hell thinks to go to yahooanswers first when they see someone being possesed? Anyways, I would call the catholic church or something because they're the only ones who deal with it. Their are also other religions who deal with possesions their own way so just call someone.

First of all, Jesus or God is very known as the person who casts unclean spirits out.Pray to God/Jesus and ask Him to cast the evil spirit out of her.That's how Jesus used His divine powers during His time on Earth.

Blast her with Yoko Ono music cranked to volume ten. A few seconds of that ungodly noise should bring her back to her right mind.

Offer her a glass of red wine. Demons can't tolerate red wine and will leave her body.

Waterboard her with a towel full of Holy Water.

lol. attack the spiritual not the physical. here is a hint, it is done through your speech. i hope you have the spiritual authority to command other spirits. invoke the name above all names.

Plead the blood of Jesus over her.

Yes you can do that, or just help her because shes having a seizure.