User blog comment:Majestic Soaring Cloud/Ichigo's destiny/@comment-10630156-20130711083154/@comment-11051098-20130711155156

As far as I know, traditionally it is the oldest person in the family who is its head. Not the strongest. So Kûkaku is probably in her right as the Shiba clan's head.

But seeing the whole bloodline of the clan would be nice, to understand just how Isshin is related to Kûkaku. She called him "uncle", at least apparently it was him.