Terry,
Can I ask a question?
Is it so much the words "I will pray for you" that riled you up, or her attitude and demeanor? I'm asking because of this: I'm trying to imagine being an athiest (which is difficult for me as I've never been one) and someone sweet, kind, and loving says they're praying for me. I might be amused at their words, but I would be grateful at their intent, which is my wellbeing was in their positive thoughts. I would probably be gracious and without going into a discussion of doctrine or religion, would say a simple thank you. Now in THIS situation, I would have probably gotten riled up as well, not so much by her words, but her intent - to change me because she didn't think I was good enough to begin with. I understand your reaction then. It is Christians like this that DO give a bad name to the rest of us. Because there are many of us that are not like that. We're not like that because Christ was never like that. I hope that your opinion of Christians can be tolerated and expanded to a more positive one by Christians other than ones like her.
Honestly, if I were in your shoes, I'd be tempted to be kind, but honest. Perhaps saying something like, "I don't mean to be rude, but your holier than thou attitude does a disservice to Christians everywhere. Try to convert me with your life example instead of your words. Let God do the converting." If she has ANY humility, your comment will strike a chord with her.
Andi