What did Avraham mean when he told Sarah that "her maidservant was in her hands?"
Why did Sarah afflict Hagar (by increasing her workload)? Was it an act of revenge?
Seforno: It was to remind her that she was her slave, and that she should treat her with due respect.
Ramban: She acted incorrectly; and so did Avraham by allowing it. 1
Riva: She had verbally afflicted Sarah. Semag says that the victim of affliction may afflict his oppressor, for the latter is not "Amisecha."
Chidushei Agados of Rav Y.S. Elyashiv: Hagar had stopped acting like a Talmid of Sarah, and considered herself to be a teacher. The affliction was to act like a Talmid, e.g. carry Sarah's clothes to the bathhouse.
QUESTIONS ON RASHI
Rashi writes: "Sarah afflicted her (va'Te'a'neha) - she gave her difficult work." What is Rashi explaining?
Gur Aryeh: We should not think that Sarah inflicted physical torture on her, for if so the verse should have used a different verb, "va'Teyaser."