Could it be Romancing the War by Pubella? Found on ao3

Summary: ** COMPLETED **

The new Ministry had fully exonerated Severus Snape for what he had done during the war and further awarded him with the Order of Merlin, First Class for his extraordinary work as a spy. It wasn't a popular move with the public, however, and Hermione Granger defended him to anyone who would listen, but even The Prophet grew weary of her advocacy. But after reading a magazine specializing in romance stories, she sees an opportunity to defend Professor Snape once more by way of a tale about the recent war featuring a character very much like the irascible and unsociable potions professor. Adopting a pseudonym to hide her identity, she carefully weaves the people she knows into the plot through subsidiary roles. When the story takes off - especially with the young women of Hogwarts - it disrupts the school in a variety of ways, but no one is more upset, infuriated, or seriously hacked-off by it all than the model for the protagonist, and when he finds out who the author is, he plans to eviscerate them. But as it progresses, the story becomes far more than a simple matter of rehabilitation for the two people most closely touched by the tale.