Harry potter and the girl who cannot die (harry potter various x fem! reader)

this is the story of a girl who cannot die
she is alive since the marauders era
she was the fifth marauder
she knew about Peter being the traitor but when she got to James and lily's house they were dead and hagrid already had taken harry potter.
she decided to go to hiding and secretly spying on Harry and make sure he received gifts on his birthday but Harry did not know who send the gifts there was always written "rexa" on the small paper attached to it.
Finally after spying on Harry for years, Harry got the Hogwarts letter and she decided to reveal herself and become a professor at Hogwarts.
Let's see the story

this is Harry Potter various x fem! reader