...oh don't get me started on my little ficcelts about Akasha again...
But since it's suppose to be said that Shinso loose their power once the blood has been extracted, theoretically, Akasha shouldn't be a Shinso vampire anymore. Which probably puts her about 2 levels above Gyokuro...unless Gyokuro did some enhancements/training.
So it should be okay power lvl-wise for the story to Akasha to come back in that weakened state. With her vast knowledge of their enemy, she'd be perfect to throw in with Tsukune's lot and to reunite the Dark Lords once more.