Mary is quite explicitly the Daughter of Sion in the account of the Annunciation: â€œRejoice, full of grace, the Lord is with youâ€, echoes Zephaniah 3:15-17.
According to the account of the Visitation (Luke 1:39-56), Mary is Sion in reference to the Temple, the sanctuary of the divine Presence in the Ark of the Covenant. Luke got his inspiration for this from the account of the Arkâ€™s ascent to Jerusalem (2 Sam 6:1-19).
Mary is also Sion through her presence in the Cenacle. If Sinai is the mountain of Godâ€™s special revelation to Israel, Sion is seen by the prophets as the mountain for the end of time, the mountain with a universal vocation, the place where all the nations will be gathered and where the Torah will be given to all peoples (Isa 2; Isa 25; Isa 60, etcâ€¦)
And the proclamation of the good news to the entire world, in the breath of the Spirit, will go forth from the Cenacle, the place where the small group of apostles were gathered around Mary, who represents Israel.
The two mountains do not nullify one another. We need them both. They manifest necessary stages in the history of the revelation of a God who accompanies human history with his loving Presence and who does not cease to surprise us through eternal newness.