It is one of our Catholic "myths" that Mary was conceived without original sin and never contracted original sin during her life - the Immaculate Conception. There is also the "myth" that remained a virgin her entire life and that at the end of her life she was raised to heaven, body and soul - the Assumption.
In one sense, I do not have a problem with these myths since are all suppose to be reflective of the new humanity in Christ. Her myth represents all the best that humanity is called to be - free from sin, living in purity of heart, and spending eternity in the divine presence.
Throughout Christian history Mary has been referred to as the Christian prototype - the ideal Christian. My issue with this is that these myths have so often been taken literally. When people takes these myths literally, they seem to take on an importance greater than the doctrines concerning Christ. When they are taken figuratively, the can be used as a help to guide us to Christ and a realization that Christ is the end, not doctrines concerning Mary.
A Faithful Catholic