TVB went through a phase during the early and mid 1980s when they let many of their contract singers try their hand at acting. Susanna Kwan, in fact, had done some acting (and not bad acting for someone whose primary work was singing) as early as the 1970s, when she appeared in such TVB modern dramas such as THE GOOD, THE BAD, and THE UGLY (THE MAN IN THE NET) and THE BROTHERS.
I think that in ROCH '83, TVB wanted to emphasize how b*tchy Lam Chiu Ying was rather than how beautiful she was, and Susanna has always been good at b*tchy roles. I thought it worked; she really made me dislike the Lam Chiu Ying character.