I was thinking today and maybe you guys should know about Madeline's mom, Mackenzie (believe it or not) Oroku. Yep her mother was raised alongside with Karai, by Shredder. Mac and Karai were raised as sisters and always believed that they are siblings.
(During the Wormquake episode) She traveled from Japan with Shredder and Tiger Claw to New York City and Karai wasn't happy about it. Mackenzie had always bested her at combat training whenever they spar together. She does know Shinigami and is friends with her. Shini teaches her magic since Mac was good at it. When she meets Mikey, things began to change and began to fall in love with him. She went to the good side and discovered Shredder isn't her real father.