Ah Hui grew up in the mountains. According to Aunt Mei, she was "wild", so sometimes when Mei Lian asked her to work, she wasn't very willing. She even intentionally messed things up, leading to Mei Lian being criticized by Aunt Mei.
During one incident, Mei Lian, mimicking her mother-in-law, physically attacked Ah Hui. Consequently, Ah Hui gradually stopped resisting her commands.
Once Mei Lian sensed success, she became more unrestrained. Later, when in a bad mood, she would take it out on Ah Hui.
Why didn't Ah Hui complain to Aunt Mei and her husband about Mei Lian's abuse in private?
Perhaps because, in Ah Hui's view, both Aunt Mei and Mei Lian were essentially the same person, with no real distinction between them.
Mei Lian abused her, and so did Aunt Mei. Was Ah Hui supposed to report to one abuser about the actions of the other?
Ah Hui knew that complaining was futile and might even result in more severe retaliation.