In her sixth year, Dumbledore makes Hermione a key figure in a plan to help Harry defeat Voldemort. (It's difficult to summarize this without spoilers— HG/SS; there's a Time Turner involved but probably not how you expect; the story really gets started in Chapter Three.)

AU. Time Travel. Snape goes back in time, holding the knowledge of what is to come if he fails. No longer holding a grudge, he seeks to shape Harry into the greatest wizard of all time, starting on the day Hagrid took Harry to Diagon Alley. No Horcruxes.

Hermione overhears something she shouldn't concerning Professor Snape and decides that maybe the House-elves aren't the only ones in need of protection.

AU, from Order of the Phoenix onwards. Hermione only wanted to learn Healing; she discovers that Professor Snape is a human being after all, and his actions dramatically shape the course of the war as events unfold. Complete.