Jesus humanity was assumed and the seed does not comes from a human father bybut thru the Divine Abba Father, while the seed of Mary comes from a pious human father who was cleansed by the merit of Christ Redemption out pouring a "spotless seed".
To believe that Mary was sanctified in the womb of St.Anne before or even after animation would implied that Mary's human nature was in the fallen state therefore not pure,virgin & immaculate and this teaching will directly contradict the upheld teachings of the Church Fathers written in the Dogma of Immaculate Conception about the spotless purity of the Blessed Virgin Mary
To her believe that Mary's humanity comes from the corrupted seed of St.Joachim will also means Her flesh was not immaculate.
To believe that the "marital act" of St.Joachim & St.Anne was tainted by lust or concupiscence meaning Mary's existence was touch by the malice of Satan runs contrary to the Dogma of Immaculate Conception in uphelding "eternal enmity" and also by the Council of Trent definition on the transmission of orginal sin.
To believe that the "first instance of conception" refers to the womb of St.Anne and not the conception in the Heavenly Realm pointing to the "conception of the Eternal Thought of God in eternity" is not in harmony with the Dogma of Immaculate Conception teaching "eternal enmity", St.Maximillian Kolbe teaching on "Created Immaculate Conception" and St.Catherine of Laboure revelation that Mary does not need "sanctification in the womb of St.Anne".
All this mystery was illuminated by St.Catherine of Laboure, Mary was not conceived in sin,and affirmed by revelation of the Blessed Virgin Mary herself to St.Bernadette Soubirous saying "I AM the Immaculate Conception". therefore does not "sanctification in the womb". SheTherefore, Mary was formed by the Holy Spirit in the order of grace a "new creature"(http://www.vatican.va/archive/ccc_css/archive/catechism/p122a3p2.htm) and specifically stated "that she be wholly borne by God's grace." as wriiten in CCC490.