Initially, Rafferty seems distant toward Shay. When Shay confronts her, Rafferty reveals that her partner at Ambulance 24 was a lesbian and used to make phone calls to her girlfriend that made Rafferty uncomfortable. In her second episode appearance, it is revealed she was a resident physician at Chicago Med but dropped out when her fiance developed Hodgkin's lymphoma; he died six months later.
At the end of Season 2, Rafferty is suspended for treating a patient against their will. As a result, Dawson regains her position as Paramedic in Charge on Ambulance 61.
Credit: Chicago Fire Wikia