"The 38-year old woman instructed the girl to sleep with her husband," spokesperson Warrant Officer Kay Makhubela said.
The girl was saved by her uncle who walked in while she was naked and about to get into the bed with the man. The man then ran away but the woman remained behind.
"Police were called and she [the woman] was arrested."
According to police, the woman owns the yard where the girl and her family are renting in Zola 3.
Makhubela said it was still not clear why the woman wanted the teenager to sleep with her husband.
The woman was expected to appear in the Protea Magistrate's Court soon on a charge of sexual assault.
