You might not realize that the concept of Mary being immaculately conceived has not been around for two thousand years, and certainly not voiced by Jesus or His Disciple-Apostles.
You have no way of knowing that. And it is implicit in Gabriel's greeting.
1854 AD the Vatican issues the dogma of the Immaculate conception. Catholics today merely imagine that has been church belief since Pentecost, without actually looking at scriptures since in 1545 AD their ‘church’ issued the doctrine of Traditions being equal to scripture in authority.