Well not for Kul Tiras, apparently, as Katherine became the Lord Admiral on the occasion of Daelin's death - so it's definitely not a case of any gender bias. Both Lordaeron and Kul Tiras seemed to follow the general rule of English male-preference primogeniture common before the 20th century. Basically put, the crown descended down the ladder to the eldest living son first, then it would pass on to the current queen or eldest daughter if a living male heir was not present.