The acting sequence with Chris paints praying Ann and the MC doing it straight after establishes Ann as the MC's slut.
A fuck toy he chooses to share with other guys. That clearly excites Ann, who's lost in her own need for sexual self exploration.
Only happy to do as her bf demands of her. The fact she already did coffee time with Chris, was happy to get wall pumped by him in front of her bf, and then take Chris in the ass, also in front of the bf, proves she's a total sub for dominant men.
Serving Tyler in the back of the car should pretty much show the MC she's easily subbed by other men.
BUT, the key ingredient being, the MC is with her.
The dorm room meeting with Chris changed all that. Which was hot. But let's have it right. The MC is balling other girls, even his own sibling/cousin.