Calling All Pray-ers: Discussion With an Atheist

Please pray for me and a friend's sister, an atheist who has engaged in a dialogue with me to discuss Christianity. I know that I cannot change her heart; only the Lord can do that. Please pray that if it's His will, He would speak (or in the case of our email exchange, type) through me, and touch her heart, opening her heart and mind to her need for the Savior, Jesus Christ.