Falling Stars and Cigarettes
Sibley doesn't need to be taken care of. After all, since she was young, she paid the bills, cleaned the house, cooked the food. She can take care of herself. Social Services disagrees and so does Sherlock. Now not only does Sherlock have to navigate the waters of fatherhood and Sibley those of being an actual daughter, but they both kind of stink at it. Of course, Moriarty would be foolish not to use this to his advantage.
(yes, I'm bringing Moriarty in, no, this is not your typical OC get's kidnapped and tortured and then everything is happy and blah blah, I promise, I'm keeping this more original!)