How does the Catholic view of Mary being without sin logically work out?

Since when was she without sin? The Bible does not say so. She was a virgin, pure in heart, humble. God asked her to bare Jesus because God saw those characteristics I listed, in her. Sounds like a Catholic view or someones individual perspective, not a Biblical one. Catholics do many things, for example put idols of heavenly things in Churches, when the Bible is against that opposed to other Christians.