She is played by Lauren Elise.
Jamie is one of many, many girls Sloane hooked up with throughout her life. Despite enjoying her company and admiring Jamie's body, Sloane decided that she wasn't the girl she was looking for, and left her in bed the following morning, no doubt leaving her feeling confused and heartbroken.
Jamie meets Sloane at a party. After introducing herself, she drunkenly flirts with Sloane, but she manages to gain Sloane's interest, and the two head to Jamie's house. They then proceed to kiss, take each other's clothes off and sleep together.
Sloane wakes up the following morning, naked with Jamie still asleep, exhausted from their sexual escapade. Sloane quickly takes a drink of whiskey and leaves. She slept with Jamie only as a means of sexual pleasure and testing her to see if she'd be a perfect replacement. She wasn't.