In Exodus 2:4, 7, Miriam signifies the truth of the church at that time and the religion near them. (Arcana Coelestia 6727, 6739)

In Exodus 15:20, this signifies the glorification of the Lord from the good of faith with reciprocity. (Arcana Coelestia 8337, 8340) When men represent truth, the women related to them represent good. Here Miriam represents external good, and so she is called the sister of Aaron, not the sister of Moses. (Arcana Coelestia 8337)