Why do Catholics believe Mary was without sin?

Hi, I have some non Catholic friends who have recently been asking why we believe that Mary is perfect, and I have given them some arguments, but they’re still looking for more. What is the best argument for why Mary is perfect? Thanks!

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Recommended Reading:**
About Mary…where in the Bible does it say…
Was Mary sinless throughout her entire life?
Do I have to believe Mary was sinless to be a Catholic?
Mary’s Sinless Nature
If Mary was sinless, why did she need a Savior?

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