Mother's secret

A mother has a big secret she is hiding from her daughter. For nearly 19 years this secret has been hidden. She has a cock. Daughter finds out when she accidentally walks in on the mother with a hot MILF.

Mother explains that she is part of an ancient race of women from an island hidden from the world where dick girls and women love together and she also reveals that she is part of the Royal family.

Daughter wants to know her mother's heritage and goes to the island. There she meets her grandmother who offers her the choice to have her own dick and join their people. All she must do is bathe in the sacred Waters of the island and she would get her own cock.

I was thinking part of this mythos should include the fact that not every woman on the island who bathes in these Waters can grow a cock. It doesn't work all the time, just works on some women. The women who do grow cocks have concubines who they impregnate to grow the population of the island. Maybe some kind of special elixir cum makes sure that the women who get fucked by the shemale can only bear daughters?....

That's some pretty complex world-building there, but if you can pull it off it would make a very interesting story setting. It sort of reminds me of the opening scenes of the new Wonder Woman movie (except for the dick part, that is).