She's not dead. The real Kuina unconsciously unlocked CoC Coating at that day. Koushirou was shocked and thus decided to hide Kuina's presence from the world no matter what. He asked his colleague, Kanjuro, to paint Kuina's doppelganger which will pretend to be dead.
While Koushiro visited Kuina's "grave", but actually met the real Kuina every night to pass on his Secret Moves, Sword Style Ougi to Kuina. In the final night, not only Kuina accomplished the Ougi, but she also managed to perma-infuse her eyes with highest degree of Skysplitter CoC Coating, unlocking The Mystic Eyes of Death Perception, an ability enabling her to kill even a God, which stemmed from the blessings of Akasha, the Mystic World.
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With this ability, she started her own journey. Before Zoro reach Laugh Tale, Kuina had visited Kuraigana Island and casually defeated Mihawk. Mihawk stated that she had far surpassed even Ryuma himself, thus entering the Realm of Gods.
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Yea thats it for Kuina's story.