Well, it would be nice if it wasn't completely impossible for women to be rulers in Islamic countries in the game, considering there were multiple actual female Islamic rulers in the game timeline. Heck, there was two significant female rulers at once in the 1210s (Queen Ahmadilidyn in Maragah, northwestern Persia, and Salbak Turhan, the last queen of the Qara Khitai Khanate, which isn't quite on the CK map but is relevant to someone who soon will be inasmuch as she had the misfortune to be holding Samarkand when Genghis Khan came knocking).
Female Muslim rulers in this time period were only slightly less common than Christian ones, really (Maat Layla ruled one of the Islamic statelets bordering Ethiopia, the fairly awesome Raziyya al-Din personally rode elephants into battle as she ruled the Mamluk Sultanate of Dehli for four years, Padshah Hatun and her hilarious self-appointed nickname killed off several of her relatives and seized control of some of the crumbling Ilkhanate in Iran, and so on and so forth).
Actually, if anything, they might do like cognatic and tie the possibility of female inheritance to culture. Women inheritance (and combat training) happened relatively often in the steppe tribes (Turks, Mamluks, Cumans, etc.) and Persia, but would have been a much harder sell in much of the Arabian peninsula and North Africa (that still leaves Arwa al-Salayhi and her amazingly lengthy rule of Yemen, though - peculiarly, the family is in the game but just changes names to a different dynasty and she never appears as a character at all despite her 37-year tenure). It probably wouldn't be wholly unfair to female Muslim rulers to get bigger negative opinion modifiers from vassals than Christian ones do - or maybe just from Zealous ones?