I'm convinced that when a person comes to Jesus Christ and commits his or her life to Him, they will become a better person than they ever were before. If your atheist friend comes to Christ some day, she'll be an even better person than she is now.
Why is she such a kind and thoughtful person? I don't know the reason; perhaps she simply has a sunny personality (as some people do), or perhaps her parents taught her to be kind and considerate when she was growing up. But I do know this: She's not this way because she's an atheist. In fact, she's this way in spite of her atheism -- because a true atheist has no real reason to believe in right and wrong, or to behave sacrificially toward others.
Pray for her, that God will open her eyes -- not only to His existence, but also to His love for her. And ask God to help you be a witness to her of Christ's love and transforming power. On the outside, she may seem self-sufficient and indifferent toward God -- but inside she may be spiritually empty and searching for inner peace.
Only Jesus can fill the empty places in our hearts, for He alone can give us peace -- peace with God, peace with others, and peace in our hearts and minds. Only He could say, "Peace I leave with you; my peace I give you. I do not give to you as the world gives" (John 14:27). Does His peace rule in your heart?