If there are other ways to be saved, why would Jesus need to die for our sins? In this case, it was cruel for Jesus to go to the cross, be crucified, and suffer for the sake of humanity if there was another way by which men could be reconciled to God. She reaches an inconsistency in her beliefs if she believes people can be saved through any other means than Christ, and Him alone.
She needs to understand the necessity of sin being paid for, otherwise we are condemned without Christ. If Jesus doesn't pay for your sins, then you will, because the penalty for sin is death, and if Christ is not standing in your stead then you have no mediator between you and God. You are guilty of your sins, and justice is called for. Christ is the propitiation for the sins of the world, but if they do not repent, they stand condemned before God (because they are guilty).
You would have to show her that we all fall short of God's glory, and there is a reason that Jesus Christ is called The Way, The Truth, and The Life and none come to the Father except through Him. He is that sufficient sacrifice that takes away our sins, the very thing that alienates us from God.