You were splinters daughter before he found the turtles and got mutated. He had left you knowing he couldn't take care of you? how could he if he looked like that, so he fled to the sewers with the turtles and left you on someones doorstep praying they would take a baby in. He never saw you again after that. You grew up healthy thinking the people that took you in were your parents for your whole life... You are now the age of 16 and the turtles are around the same age Raph- 19 Donnie- 18 Leo- 18 and Mikey- 17. While the turtles were messing about (aka Leo) in the dojo they could hear Splinter talking to himself when they listened they heard him talking about.. you.. When the turtles realized they had a sister.. well not by blood but they see Splinter as their dad so you must be their sister. They all calmed down and looked at each other... why would Splinter never tell them. They decided to talk to Splinter about it, and when they did they could tell he was upset and with a guilty look on his face he said "I'm better with the family that is now looking after me" but Leo, Donnie, Raph, Mikey wanted to find out about you, so they got the house from Splinter that he last put you and they went looking. And they stayed on the roof of the other house waiting for something.. Until they saw a teenage girl walk out the house in (your favorite clothes) that were your (f/c). Your hair was out your eyes as you started to walk down the roads of new York down the the high school. What will happen next? Du du duuuuu you'll have to find out :D