Her best friends are Stassi Clayton and Kelly Krueger.  They lived in the same neighborhood, and have known each other since they were three.

[Six month plan: Stassi and her husband almost break up, but get counseling and repair their relationship.  Kelly grows increasingly unhappy with her marriage, resists having an affair, but discovers her husband is having one and she divorces him.]

At the gym, she is acquanted with Sarah (a superficial bottle blond who wears make-up while exercising) and Giang (with the fashion model body and empty head).

Her usual partner when working is Bill Hamilton ("Bill H."). He and Jenn knew each other in grade school, and have worked together for more than a year.  Bill Lambert ("Bill L.") is another paramedic she has a lot of contact with.  Bill L. seems to have a crush on Jennifer, but the feelings are not reciprocated as she considers him to be a serious jerk.

Jennifer has an on-again off-again we're-not-really-dating relationship with one of the doctors at the hopital.  They've been like this since she came to the hospital, and he is five years older than she is.  For now, at least, I'm leaving him largely undefined, although I tend to picture him as Asian, with a runner's body and interest in athletics and physical fitness.