History

• She has a fairly standard upbringing as a kid. She lives with both of her parents in an apartment building in Manhattan.

• She met the turtles when she was a little girl on her apartment rooftop's basketball court.  The guys were playing when she wandered in and didn't bat an eye at their appearance.  They've been friends ever since.

• One assumes that between the ages of 12-16 they do a lot of standard teen hangouts-- movies, pizza, etc-- and some nightly rooftop shenanigans, none of which being particularly dangerous.  April is basically their unofficial big sister as she's older than all of them and she takes this very seriously.

• They meet Mayhem, a cute little weird cat-dog-hybrid yokai on the run from bounty hunters, and they try to protect him but fail.  When they vanish through a portal April dives in after them without thinking. The turtles find a way to go after her, at which point she has already scouted the place, shows them where Mayhem is being held, and shows them to an armoury where they can get new mystic weapons. Once they rescue Mayhem, he goes home to live with her.

• After this, show canon has things get a lot crazier.  April isn't there for all of it, and when she is she's often support or a friendly ear.  She has a slew of part time jobs none of which she can seem to keep, but has no qualms about this and often uses the keys to her old workplaces to help the guys out / gives them old wifi passwords, etc etc. 

• In the grand finale of the series, she comes back to the destroyed lair only to find a dying Karai-- the ancestor of the Hamato clan-- who imparts her soul to April.  When April protests she is not a Hamato, Karai tells her you have always been one of us.  With Karai's help, she helps the guys connect with their ninpo for the first time and then helps them fight Shredder one last time.  At the end, Karai leaves April's body to reunite with her dead father, and her connection to the ninpo fades-- but one assumes it can be reignited again.

• In the movie, April again plays support, but gets the turtles out of a couple bad situations with her discovery of a herbicide that can burn away Krang tissue.  In the end fight, she leads the ground team in getting close to the portal so they can take it out.  Sister Krang tries to stop them, and Splinter and Casey keep her engaged in the foundation of a partially constructed building while April uses the nearby crane to knock the building down on top of her.

• She comes to Folkmore from the very end of the movie, where she and the turtles are eating pizza on top of a building and watching the sun go down over a newly repaired New York.