At last, she arrived in time for the ball held that night, and everybody was charmed by her looks and manners.

her 是代词 she 的所有格形式，表示"她的"。 looks 是名词 look 的复数形式，look 本义是"看、外表"，复数形式 looks 特指"外貌、容貌"。 her looks 指"她的外貌"，强调整体容貌给人的印象。