Ok here is what you do. DO NOT come at her from a critical place towards Scientology. That will make things worse for both of you. She has only been in for 6 months, and that is what you have on your side. Your daughter is becoming addicted to a huge system of support as well as a hypnotic state that Scientologists get put in by Scientology auditing. That system is telling her that Scientology is more important than anything else and that so is she, she thinks she is saving the world.
What you need to do is appeal to her humanhood. Peel her away from Scientology for at least a few days to come and see you BEFORE you start talking to her about it. That way you can really sit her down and talk to her. Do not make clear the intentions of the visit, i know that sounds deceptive but you dont want to lose your daughter. I may sound overdramatic, but in my experience there is a high mathematical likeliness of losing someone in this situation. So have finesse about it. Also, be optimistic, and if it doesnt work the first time, try try again and all that.
You need to do serious research about Scientology and have key points to present to her. Here's the wiki page that will give you the basics about operation snow white, feel free to look it up after there
http://en.wikipedia.org/wiki/Operation_Snow_White
Bare faced messiah is the true story of L. Ron Hubbard. This website contains all or at least most of the book i think. If not then a very good outline. It contains pictures and sources and citations, so you might want to check it out
http://www.xenu.net/archive/books/bfm/bfm01.htm
That would be a good start. I also recommend checking out xenu tv on youtube. Look specifically for videos of how Scientology "handlers" treat protesters.
Ok, there you go. Good luck.