Optimus' sister has a sparking to an unknown bot, and after her death Optimus sends the young femme to Earth for her own safety. When the Autobots take refuge on Earth years later, he still has a small hope of finding his niece.
Shayleah is the adopted daughter of Will and Sarah Lennox, best friend of Sam and Mikaela. At one point her only challenges in life were keeping Sam from catching her out as being Cybertronian and liaising between him and his crush- her best friend. That is until the Autobots arrive on Earth, searching for the AllSpark and she discovers who her sire is, leaving her invested in both sides of the continuing war.
A Bayverse transformers fic
Thanks to @HedgehogTurtle for the awesome cover