Akasha wasn't even trying to attack Akuha then when they fought. Like Fuhai said when they watched the memory record of the fight - Akasha could never fight against someone she regarded as a daughter.
When Akasha went on the offensive against Alucard, the look on Akuha's face said, "Oh shi- If she had hit me, I would have been screwed!" Her best trump card attack did NOTHING to Alucard but Akasha's one kick literally disintergrated the freaking monster tentacle. Akuha realized she was genuinely and exponentially outclassed by Akasha. One does not take on the leader of the power trio that saved the Youkai world from a great evil without being at least comparable with the same 'great evil' that they've already defeated or you're just wasting their time.
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She knows that if she takes on a Dark Lord, that she'll have to be fully prepared - she now knows first hand what the power of a Dark Lord is truly like and it's nothing like what the youkai running around nowadays have going for them.