no heirs despite having children of both genders??

hi so im pretty new to the game, got it for christmas, and im doing,,,ok as the 867 start in africa, i got to ruling kano and having it be pretty big, but for some reason i dont have an heir, i have both sons and daughters of my own line but none of them are my heirs? i have female preferred succession and matrilinial marriage, and this is the startiung characters daughter, so she already inherited once, wich worked fine, but why doesnt it now??