Theory about Glinda.
Ok so mother South is the mother of all witches and she supposedly died 20 years ago. There are young witches under 20, and West assumes her mother is still alive. In the books isn't Glinda of the South? I was just thinking what if Glinda took on the mantle (powers) of her mother after death and she gave birth to those girls with the help of Roan (Lucas).
Nemo Unus Animabus Carnem!