How do I get my point across without starting a heated debate?

I have a friend who's involved in a church who's leader I have reason to believe is leading his followers astray. She e-mailed me some of his views and I found in the Bible direct disagreements to what he teaches. I want to let my friend know this, and I want her to realize that she is in error. The problem is, she is a very devout follower of this man and I don't like stepping on people's toes. Also, english is her second language. Would it be better to explain these contradictions I've noticed via e-mail, or face to face? Also, how should I lead in to what I'm about to tell her, knowing it's stripping away th foundation she's been standing on for years now?