
The Catholic church has an entirely different view of Mary than do 
"most" other Christian churches (those with parallel beliefs
notwithstanding).  Christ, by most accounts, is the only sinless
person to ever live.  I too, have trouble with a sinless Mary
concept just. 
As for the related issue of the "original" sin - only Adam and
Eve will answer for that one.  My children do not answer for my sins,
certainly I only answer for mine.