I don't think Zeitgeist was the best recommendation to be honest. Has quite a few inaccuracies hasn't it? For books I would recommend two; the best in my opinion. 1) God is not great by Hitchens and 2) the god delusion by Dawkins. They both are fantastic. Especially the first one.

Any video on YouTube of Seth Andrews.

Why can't people think for themselves and explore themselves? Are people just empty sponges just waiting to soak up what's offered them.

I would pick something positive. Maybe Stephen Pinker.

Joseph Campbell.

No sacred Cows   by David McAfee
Atheist Manifesto by   Michel Onfray
and The Portable Atheist by Christopher Hitchens

Anything by Voltaire.

Check out Dark Matter videos on YouTube. They are hilarious and highly entertaining but also brings up very valid points.

The Bible, if that doesn't turn you into an atheist nothing truly will.

Have her read Good Without God, a book about the humanist beliefs many atheist share.

Tell her to read the whole bible. She'll come away an atheist.

first person account of how one Christian left the faith and why, became Atheist.

Tell her to read bible then read Hitchens God is not Great.

Another option is The Evolution of God. It's a factual and gentle introduction to the history of Christianity. From an archeological perspective. It will help her to understand the true history (in a positive way) of Christianity and that it's really mythology.

Ask her to join here and I am sure our pooled resources can give respectful responses to any queries with clarity. There may be questions that challenge our personal viewpoints which can only be good. Books of that kind are great for information but informed discussion is a much better way to understand a topic I have found.

Suggest that she watch "Letting Go of God", by Julia Sweeney. It's a hilarious and entertaining story of a woman's journey from a good Catholic girl to an Atheist.

Here's the trailer:

I tell my Christian friends to think about the thousands of gods people around the world believe in, and understand that they believe in just one more god than I do.
All the gods are imaginary to me, just like all the other gods are imaginary to my christian friend.

Easy but thought invoking read for me was 'Letter to a Christian nation' Sam Harris

What has already been said plus:

God's Debris by Scott Adams

Sock by Penn Gillette.

Both are quick reads and super easy to digest.

I wouldn't advise her to watch Zeitgeist. There are a lot of made up facts presented in it. If she is curious, she'll be better advised to seek out honest books or sources.

Have her read "A New Earth" by Eckhart Tolle

Bill Maher's movie "Religulous" is good too. Penn Gillette has a great collection of essays "Every Day is an Atheist Holiday". [goodreads.com]

The important thing to understand is that atheism is not an "ism", in terms of being a dogmatic ideology. It is simply the rejection of religion and deities. I would recommend that she read about existentialism.

The God Delusion
God Is Not Great
God- The Failed Hypothesis

The Age of Reason by Thomas Paine - an easy-to-read narrative of biblical inconsistencies, written by a former Quaker. Zealot: the Life and Times of Jesus of Nazareth by Reza Aslan - doesn't deny the birth of Jesus and explains the genesis of the bible. The End of Faith by Sam Harris - explains how organized faith cannot mesh with rational thought and its role in terrorism. Should probably also be said that these aren't atheist guides, but rather analytical pieces to provide insight as to why some might reject Christianity, and as such, not as combative or as antagonistic as someone like Richard Dawkins.