The Immaculate Conception means that Mary, whose conception was brought about the normal way, was conceived without original sin or its stain—that’s what "immaculate" means: without stain. The essence of original sin consists in the deprivation of sanctifying grace, and its stain is a corrupt nature. Mary was preserved from these defects by God’s grace; from the first instant of her existence she was in the state of sanctifying grace and was free from the corrupt nature original sin brings.
When discussing the Immaculate Conception, an implicit reference may be found in the angel’s greeting to Mary. The angel Gabriel said, "Hail, full of grace, the Lord is with you" (Luke 1:28). The phrase "full of grace" is a translation of the Greek word kecharitomene. It therefore expresses a characteristic quality of Mary
The traditional translation, "full of grace," is better than the one found in many recent versions of the New Testament, which give something along the lines of "highly favored daughter." Mary was indeed a highly favored daughter of God, but the Greek implies more than that (and it never mentions the word for "daughter"). The grace given to Mary is at once permanent and of a unique kind. Kecharitomene is a perfect passive participle of charitoo, meaning "to fill or endow with grace." Since this term is in the perfect tense, it indicates that Mary was graced in the past but with continuing effects in the present. So, the grace Mary enjoyed was not a result of the angel’s visit. In fact, Catholics hold, it extended over the whole of her life, from conception onward. She was in a state of sanctifying grace from the first moment of her existence.
Catholic Christianity does believe that Mary was a sinner. Not an ACTUAL sinner, but a POTENTIAL sinner who was redeemed by God from the moment of her conception so that she never fell into sin. So yes, Mary was redeemed, but she was also predestined by God to bear his Son and so she was upheld from falling into sin.
Can you show from scripture where it says Mary had relations with Joseph and that she birthed other children?