Don

Nyland translates Gal 4:7 as “Consequently, you are no longer a slave but legally adopted, and since you are legally adopted, then by God’s act you are an heir.”

She seems to be saying the point of the verse is adoption and being an heir and not being a son, that is incidental words to express the big idea.  Or another way of looking at it is similar to 1950’s English, sometimes in Greek (and 1950s English) a singular man can be a woman, it depends on whether it is a man inclusive or a man exclusive.