she'd be his half sister from his dad's 2nd marriage, aged anywhere from 18-28. jd probably leans on her a little too much to balance his brand of crazy - whether she is happy about that (or even whether she likes him or not) is up to you. their family is super close (jd's mom lives in the same house as their dad/your girl's mom), but i left pretty much everything else open so there'd be room to collaborate.