Upvote:1
Its really not that difficult. At that time in Israel she would have been considered the daughter of both he genetic father and his genetic father. It was common practice to list the names of genetic fatherhood for several generations. There are many instances of that in the Old Testament. In the book of Ruth you will find her listed as the daughter of Mordaci; even though he was actually her uncle.
Since Anah was a common name listing the genealogy of the individual was a way of describing the particular individual. That is the reason for the listing of Zibeon as Anah's father in 36:24; and Sier as the father in 36:20. Quite simply they are two different individuals.
Hope this helps.