Harriett Jasmine Potter, was left on the wrong doorstep the night after her parents were murdered. Instead of No 4 Privet Drive in Little Whinging, she is left on the stoop of No 4 Privet Lane in a completely different town.
The denizen of the home she was left at was a drunk widower, who decided, what the hell, guess I got a kid now. His name was Marshall Quinnzel, and he named the kid Harleen after his dead wife.
Set to move to America to start a new job and a new life after the tragic death of his wife, Marshall takes the baby with him. He's got some shady ass friends that help him make a fake birth certificate for the kid, and there it is, off to Gotham City New Jersey.
Harleen, or Harley as most call her, had a shady upbringing, filled with petty crime and weird things happening to and around her.
Being out of England, Harley doesn't get an invitation to Hogwarts, and when ilvermorny contacts Marshall, he declines allowing his daughter attend stating financial difficulties. Both of them are obliviated of the knowledge of magic existing, and they go on their merry way.
Harley is super smart, but her knowledge is mostly dedicated to surviving and bringing in as much money as she can so she can have enough left over to take care of herself after her father takes most of it. School is just that place she shows up sometimes to take stupid tests that are way too easy, and be told she'll never amount to anything. Marshall gets pinched when Harley is eleven, and she becomes a foster child. She bolts after a few months when her latest foster father tries to climb into her bed in the middle of the night. She makes sure to castrate him in the way out, make sure he'll never do it again.
She lives in the streets for a minute, until she's taken in by one of the local street gangs. She wastes little time becoming invaluable to the boss, and things are going great for a few months, until the asshole sets her up as a patsy in a drug deal gone wrong with one of the bigger gangs.
She leaves the fucker giftwrapped in his own intestines on the driveway of the rival gangs hideout, and skips town for a minute.
She comes back with a shiny new highschool diploma a year later, and picks up her pops in her new car, that she definitely did not boost and switch the plates for on her way to pick him up from the clink when he's finished serving his sentence.
Her pops joined a gang while in the inside, and is apparently now gainfully employed by some whackadoodle that everyone calls "The Penguin" really though, what's Gotham coming to, that instead of nice wholesome gangsters and street thugs, you now got whackos running around in spandex and pleather giving themselves names like they's in the funny papers or somethin.
Harley does a few jobs with her pops though, easy way to earn some scratch, while moonlighting as a college girl going for a PhD.
Through some...creative handling, Harley gets herself a shiny new doctorate in less than a year, and all she has to do was ace a few tests and fudge a few details.
Boss man gets her hired on at Arkham, exaggerating her age a little bit, so she can be his inside girl to help spring a couple buddies of his.
While there, she makes the acquaintance of Mr. J, and she decides to spring him too, only, he decides to keep her for himself, and dumps her in the vat of chemicals he'd experience his own rebirth from.
Her time with Mr. J is cut horribly short though, when a bunch of clowns waving sticks and wearing dresses come and kidnap her.
They try and convince her she's some missing kid named Harry(blek) Potter, and she had to compete in some magical death tournament, or lose her magic.
And she thought Mr. J was cracked.
Still, the rubes eat on solid gold plates and can make things out of nothing with those funny little sticks of theirs, so she decides to see what the whole thing is all about, and if she'll be able to take them for all they're worth.