"Even at seventeen, Dolores was judgemental, prejudiced and sadistic, although her conscientious attitude, her saccharine manner towards her superiors, and the ruthlessness and stealth with which she took credit for other people's work soon gained her advancement."
She saw through the girl's saccharine smile and knew that her best friend's newfound partner was up to no good. She wanted to confront him about it, however, she hasn't seen him this happy in a long time. So, she walked away knowing that she couldn't risk his happiness for hers.