I'm trying to find my friend's biological father. She shares 605cm with a woman who it seems is her half-1st cousin (their fathers have the same father but different mother). My friend's father was 100% Lebanese, but this woman is only 25% Lebanese. The grandfather was married to a Lebanese woman and then a European woman. So it seems the Lebanese Grandfather had my friend's father with his Lebanese wife and then the cousin's father with his European wife.

However, my friend also matches at 2041cm with a woman who was born in 1958 (my friend was born in 1962). She is also 50% Lebanese. If they share the same father, that means he must've conceived her half-sister when he was 12. Is there any other possible explanation rather than them being half-sisters?