Since Mary believed in Her Son, don’t you think she IS now sinless? And doesn’t your God have the ability to see all of time as a volume, so that Mary would be afforded at least the same deference that Abraham received, whose believing/faithing was counted for him ‘righteousness’? ... And for the record, I’m not a Catholic, though I am catholic.
No. No human being is forgiven because they are sinless. Humans are FORGIVEN of their sins by faith in Christ, in part because He has already redeemed us from the slave market of sin.
FWIW, do we have any passages proving Mary was faithful after His birth? The few passages we do have regarding her manifest the role of woman with respect to man, but also consider how Christ treated her as both Son of Man and Son of God. When Christ was on the Cross, telling Mary to behold her son, IMHO, this manifests a very responsible and humble witness to his mother. Considering the dual of the argument, had she been as sinless, as some purport, what lesson was He attempting to communicate.
Instead, IMHO, it reveals He may have been giving a lesson to his mother to correct her past way of thinking.