When we mention the name of prophet, messenger or their righteous companions:
1. Messengers: Adam, Enoch, Noah, Lot, Abraham, Ishmael, Isaac, Jacob, Joseph, Aron, Moses, David, Solomon, Job, Ezekiel, Jonah, Elias, Elisha, Zakarias, John, Jesus and Muhammad we say 'Alaihi As-sallam': "peace be upon him"
2. Angels: Jibril (Gariel), Mikail (Michael) etc we say 'Alaihi As-sallam': "peace be upon him"
3. Righteous women: e.g. Mariam mother of Jesus, and other female companions of prophets we say Radiallahu anha: "God is pleased with her"
4. Righteous men: male companions of prophets we say Radiallahu anhu: "God is pleased with her"
Summary:
Alaihi As-salam for Messengers and Angels: "peace be upon him". Radhiallahu anhu goes for the Anbia i.e. all prophets (male): "God is pleased with him".
Radiallahu anhu goes for males Companions and those around prophets: "God is pleased with her".
Radiallahu anha goes for females Companions and those around prophets: "God is pleased with him".
Sallallahu Alaihi Wasallam for Nabi Muhammad (S.A.W.) only: "God grant him peace and honour".
So for Mariam (the mother of Jesus) we say RadiAllahu anha: "God is pleased with her"