Moka is
of the Shuzen family but she is not a Shuzen ... if that makes any sense. When it comes down to it, all the marriage did between Akasha and Issa was to attach the Bloodriver name to the Shuzen family. The Shuzen Family, though prestigious, couldn't 'absorb' the Bloodriver name/family because of the sheer amount of power wielded by Akasha, both physical and possibly political - she's a Shinso - she was a venerable Queen, unattatched to a clan or group. She didn't marry into the Shuzen Family, the Family married her.
Why else couldn't Gyokuro do anything directly to Akasha?
If she married into the family, Akasha would have fallen to #2 wife beneath Gyokuro - and oh hell, wouldn't the psycho have had fun being able to order a Shinso around by virtue of their status as wives to Issa. Akasha submitted to Issa voluntarily, but I don't think that she was going to put herself beneath Gyokuro for anything. Akasha probably even told her that she considered the both of them to be 'equal as wives' but Gyokuro probably didn't see it that way. Akasha was a Shinso - there is no being equal to a Shinso. Issa would be stupid to go against her word, even if it was just a suggestion or a hint. Even if Akasha tried to come to terms with her, Gyokuro most likely just saw Akasha as a Shinso and nothing else - an immortal monster with power unrivaled that wanted peace.
I say that Akasha needs to have a few 'befriending' lessons from Nanoha in order to properly deal with Gyokuro.
... The thought of Akasha unleashing a Starlight Breaker is...
*Reality Breaks*