Mother Teresa is someone who proves God exists in a way. She shows us as well as anyone the true nature of Christianity and what it means to love our neighbor. Grappling with the fact that such immense good comes from our Faith means that we have to grapple with the idea that that is how God really wants us to live. You never hear anything about Catholics who do negative things "losing their Faith" or not being good Christians, but the one woman in recent years we can look at and say she absolutely and beyond a shadow of a doubt had a true Faith needs to be attacked, because it would be scary to admit the Love of God.
Even I, when I was Protestant had to try to demonize Mother Teresa in some way. I couldn't grasp the fact that such a wonderful and pure person could be Catholic. It didn't make sense how she would be going to hell after such a life. I'm just thankful that God has given me the graces to come to a better understanding of Faith and Christianity now.