
   Just a quick question. If Mary was Immaculately concieved, so she
   could be a pure vessel, does this mean that she was without sin
   and, therefore, the perfect (meaning sinless) female human being?
   Is this why she is held so highly in the Catholic Church despite
   it's basically patriarchical structure?

She was immaculately conceived, and so never subject to Original Sin,
but also never committed a personal sin in her whole life.  This was
possible because of the special degree of grace granted to her by God.

She is regarded so highly because of her special relationship to God,
and everything that flows from that relationship.

The Catholic Church sees her as the new Eve.  (The Fathers in the
early Church use this particular figure a lot.)