My Daughter, My Wife...
As shown, father-daughter marriages were not unknown but not a common occurance in the royal family. At a guess, upon the great royal wife's death the next queen with the nearest royal blood would be elevated to chief wife ( in the case of Mutemwiya, after Yaret's death, she was already a second wife and the mother of the king's eldest son).The eldest daughter of the newly elevated queen could appear to be seen as an heiress, so her father would marry her to ensure an uncomplicated succession with the official heirs of the deceased great wife. While there is no established proof for this theory, it would explain this unusual practice.
Sometimes, no kings wife was elevated after a queens death (as in the case of Amunhotep II, when his second great wife, Sitamun I died). Although unusual, this would also ensure a smooth transition of power to his established heirs on his death. In almost every one of these instances, the daughter married was not an heiress by the great wife. This daughter would be reserved for the heir to the throne. This however, was not always the rule.