This theory doesn't say that Harry was a girl.
I've never considered myself as a theorist. That's why you can see my bio doesn't say "theorist". It says "supplier of film theories". And not all the stuff on my profile are theories. But most of them are and those theories usually don't come from me. The only one I've come up with is my Back to the Futures II & III Took Place in Marty McFly's Dream Theory.
But here I am, with a new theory that I think might be plausible.
Many in the Wizarding World know Harry Potter as "The Boy Who Lived". This is because he was the only person that had ever survived the Killing Curse and that curse was done by Voldemort. This led to Voldemort's downfall and the end to the First Wizarding War.
Harry discovers this ten years later as an eleven year old boy. Hagrid tells him the whole story. BUT AT ONE POINT, Hagrid says this:
"No one ever lived after he decided ter kill 'em, no oneexcept you, an' he'd killed some o' the best witches an' wizards of the age -- the McKinnons, the Bones, the Prewetts -- an' you was only a baby, an' you lived."
Let's take a look at the names Hagrid lists: McKinnons, Bones, and Prewetts. So that means that Voldemort murdered the families with the surnames: McKinnon, Bones, and Prewett.
In both the book and film version of Harry Potter and the Sorcerer's Stone, we see a girl named Susan Bones being sorted into Hufflepuff.
Btw, that girl is portrayed by Eleanor Columbus, the daughter of the film's director, Chris Columbus (the Chris Columbus that didn't kill any Indians).
But look at her name! Susan BONES! Voldemort murdered her family, but like Harry, Susan Bones lived and went to Hogwarts the same year as Harry!
Like the great Marty McFly said: "HOLY S***!"
Now, exactly why she didn't get credit. I don't know.