The problem is that the Bible, when read literally–which is the way most uneducated, elderly, grandmotherly-type Christians interpret it–doesn’t leave room for nice, sincere atheists. One is either a follower of Christ, or a worshipper (or at least tool/victim/pawn) of Satan.
Consider:
Jesus, when speaking about his group of disciples in Mark chapter 9, says that “Whoever is not against us is for us,” (v. 40). Presumably the converse is true: Whoever is not “for” Jesus and his followers is “against” them.
In Revelation 3:16, Jesus is portrayed by John as being pretty black-and-white on the subject: “Because you are lukewarm—neither hot nor cold—I am about to spit you out of my mouth.” Not even people who are apathetic or agnostic are OK, in Jesus’ eyes: much preferable to be either zealously Christian, or zealously anti-Christian.
John speaks similarly in 1 John 4:3: “[E]very spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world.” So, don’t acknowledge Jesus? That’s cause you’re being inspired by the antichrist.
Paul writes in his first letter to the Corinthians that, “For the wisdom of this world is foolishness in God’s sight.” (3:19) He makes similar implications elsewhere, suggesting that there can be nothing good, holy, or wholesome outside of God/Christ. So, little or no room for decent atheists there.
James was even more direct on this point: “You adulterous people, don’t you know that friendship with the world is hatred toward God? Anyone who chooses to be a friend of the world becomes an enemy of God.” (4:4)
So don’t be angry at your co-worker; she’s just being a thorough, consistent Christian.
Be angry at Christianity.