Big Bad Sis (1976)

Ah Ying (Chen Ping) is a former gangster trying to lead an honest life, and occasionally using her fighting skills to help out the girls in the factory where she now works. She befriends young colleagues Chong Lee and Shao Yin-Yin, teaching them self defense because "girls can't be weak anymore". Trouble starts when her old gang finds out where she now works.