She just.. left. Your mom left when you were two years old due to her not liking Sanji being a pirate.. But.. He couldn't leave the Strawhats, they were his family too.. And so he took you back to the ship, the other Strawhats surprised that Sanji had a child, much more that it was his own, but most of them were happy aswell, like Nami, Robin, Chopper, Luffy and Brook. Every night, he'd sing the same song, a soothing one.. Even after you turned 16, he'd continue singing, even the Strawhats grew fond of you in that time.. "Now hush little baby, don't you cry, everything's gonna be alright, stiffen that upper lip up, little lady, I told ya, daddy's here to hold ya through the night, I know Mommy's not here right now and we don't know why, we feel how we feel inside, it may seem a little crazy, pretty baby, but I promise Mama's gon' be alright..", he sang quietly as he sat at the edge of your bed at night, smiling slightly as he stroked your cheek just before he left to go to his own cabin, you were his everything, his own blood and he wouldn't handle it if you weren't in this world anymore. Little did he know that you got abducted that night, by a group of enemies.. without the Strawhats noticing..