One possibility is to draw upon the Fatherhood of God. Good human parents, you might point out, do not rescue their children from every difficulty they encounter or from every bump and bruise they may suffer—even when it is within their power to prevent it; instead, they sometimes allow their children to experience the natural consequences of their choices. Likewise, God is no less all-loving and all-powerful if he allows us to experience the natural consequences of our choices. Obviously, this analogy doesn’t account for the innocent suffering of those who have committed no wrongdoing. That is where Christian revelation enters with its understanding of vicarious responsibility for sin, vicarious atonement for sin, and the redemptive value of innocent suffering offered up in union with Christ’s sacrifice on Calvary. Nevertheless, you could start by appealing to common human experience to see if that opens the door to a discussion of the Christian understanding of suffering and death. One of the most powerful secular explorations of suffering and death in recent years has been J. K. Rowling’s Harry Potter series. Some argue that the series draws on Christian imagery and Christian themes, but it does not explicitly mention Christ or Christianity, and it has been popular with audiences uninterested in Christian literature. If your friend is not interested in an explicitly Catholic explanation of suffering and death, perhaps she will be interested in a secular story that incorporates those themes.