...point them to this.
It is coincidental that I came across this on CAEI because this was the exact thing we were talking about in my Catechism class. God is all powerful and at the same time, God permits evil to win a round so that mercy and forgiveness may prove their greater might. Don't believe me? Hear it from the Catechism:
272 Faith in God the Father Almighty can be put to the test by the experience of evil and suffering. God can sometimes seem to be absent and incapable of stopping evil. But in the most mysterious way God the Father has revealed his almighty power in the voluntary humiliation and Resurrection of his Son, by which he conquered evil. Christ crucified is thus "the power of God and the wisdom of God. For the foolishness of God is wiser than men, and the weakness of God is stronger than men." It is in Christ's Resurrection and exaltation that the Father has shown forth "the immeasurable greatness of his power in us who believe".
273 Only faith can embrace the mysterious ways of God's almighty power. This faith glories in its weaknesses in order to draw to itself Christ's power.113 The Virgin Mary is the supreme model of this faith, for she believed that "nothing will be impossible with God", and was able to magnify the Lord: "For he who is mighty has done great things for me, and holy is his name."
274 "Nothing is more apt to confirm our faith and hope than holding it fixed in our minds that nothing is impossible with God. Once our reason has grasped the idea of God's almighty power, it will easily and without any hesitation admit everything that [the Creed] will afterwards propose for us to believe - even if they be great and marvellous things, far above the ordinary laws of nature."