Jesus fulfilled the Law, and the Law ended by His death and rising. Jesus was sinless and the only one who could keep the Law. To not keep the Law in the OT was a sin. Peter in Acts 15:9-11 said that no one (but Jesus) could keep the Law, and that salvation was then by faith in Jesus Christ.
Catholic doctrine is that Mary was sinless and was redeemed upon her conception, so her salvation was, according to Catholic doctrine, in advance of the death of Jesus.
If no one could perfectly keep the Law but Jesus, and Mary was sinless and already had salvation, does this mean that Mary was not required to follow the Law? By not following the Law she wouldn’t have been sinning as she would have already been living under the grace of Jesus the Son of God before the conception of Jesus.
So, is it Catholic doctrine that Mary was sinless only by the grace of God, and not by grace combined with following the Law perfectly (something she couldn’t do, as only Jesus could)?