The Interpretation of Galatians 4 Verse 24

In Galatians 4 verse 24, we can see some of the problem here. These women are two covenants. One is from Mount Sinai bearing children for slavery. The Jerusalem that is above is free and she is our mother. It's said to be an allegory. You'd also have to make Sinai into who's Sinai. Is there a third God the mother? What is this? It just doesn't work.