Sydney was the fiancée to Jamie Reagan in season 1 until their breakup in episode 8 "Chinatown". During her time in season 1, she was a Junior Associate at a law firm and after her breakup with Jamie, she takes a job in London for 6 months.
She smokes when stressed or angry (Pilot).
She's happy Jamie does something he loves but hates that she comes second to his job. (Privilege)