Memories

Arianna Walsingham is a pureblood witch that Dumbledore asked to come into Hogwarts be an extra professor of the defence against the dark arts as the classes got too big for 1 professor. Recently a new rule was implemented that every house will have a "deputy head" in case the house head was unavailable, (or in some cases, are too terrifying to talk to, *cough* Snape *cough*) Arianna is a former Hogwarts student graduating best in Hogwarts history in defence against the dark arts and second best in potions because of none other than Severus Snape.

Snape and Arianna were good friends that were in the same Hogwarts year and classes. She stuck by his side even when Lilly left him. Unfortunately, due to events after graduation all memory of her vanished from him. He no longer remembers her, and she knows this.

Yet maybe, just maybe, she can make him remember her again. Somehow.

(Right so this will kinda rewrite Harry Potter as we know it cause it's adding another character. Please don't hate me. And this does take place when the Golden Trio is attending Hogwarts during the events of Prisoner of Azkaban and Goblet of Fire might extend it but not sure. So think Snape looks more like his book age of 35-ish. Just look at pic to get what I mean.)