Again the problem here is that you are seeing being cleansed form sin as being saved. It doesn’t matter when she was cleansed from all sin, the problem with OS is that it is the post-fall condition of man. If Mary doesn’t have OS, she doesn’t share any nature with us, thus Christ doesn’t share any nature with us, thus his incarnation has no point at all. Also that Mary was already saved pre-fall.
We believe St. John the Baptist to be sanctified in the womb.
Baptism isn’t only for the remission of sins, it is also joining ourselves to Christ’s death so that like Christ we may be raised up. Every baptism in the Orthodox Church we sing the Baptismal Troparion:
As many as have been baptized into Christ, have put on Christ. Alleluia!
Again, in Orthodoxy, sin isn’t only committed offences, it is death as well. We are not reversed into a pre-fall state, but rather because we are headed to our graves we are united into Christ by putting on Christ, so that by His grace we will trample down our death by our own death like He did. That is why in the Creed the Baptism immediately precedes the profession on the belief on the resurrection, they are connected.