I realize this may not be the answer you hoped for—but in reality, you can’t logically explain it to her, because it isn’t logical for you to turn your back on the greatest truth in the universe, which is God.
Let me give a simple illustration. Suppose you and your friend were hiking in the mountains and came to a sharp cliff. At first it looked like the trail ended and there was no way to get across the valley. But then your friend pointed out that the trail turned and continued down the mountainside. What would you do? Would you step off the cliff, saying you didn’t feel any need to believe in gravity? No, of course not. Instead, you’d follow the trail.
You see, every day you follow the laws of nature because you know they are true. Why, then, do you dismiss the greatest truth of all—which is God? Why step off the cliff (so to speak) of unbelief? The Bible bluntly declares, “The fool says in his heart, ‘There is no God’ ” (Psalm 14:1).
How do I know God exists—and not only exists, but loves us and wants to help us? I could give many reasons—but the most important is Jesus Christ. He was God in human flesh, sent from Heaven to bring us back to God. During this Christmas season, let go of your pride and your desire to run your own life, and open your heart to Christ’s love and transforming power.