A best friend, preferably female. PB is up to you, the idea was for them to have been childhood friends, and when she moved away they were separated until her BFF turned 18 and moved to New York to attend college with her. They'd be un-romantic soulmates, in essence. She's probably Sam's kids' godmother.
A younger half sibling or two. Sam's father died when she was 8 so I'm toying with the idea of having some younger siblings from a second marriage of her mother's. Not picky about genders, names, or PBs here. Brainstorming is love! You'd also have her hubby and niece to interact with.
Her nephew! zogeller needs her big brother. Sam would have been a motherly figure for him after his mother's death about 15 years ago. Even now that he's all grown up!
Co-workers in the D.A's office, the D.A. included!