You need to remember first you keep her passport is not illegal you have her request letter.
If she repost loss of the passport she needs time to process in consulate that means she cannot leave HK immediately . (Indonesia Consulate Morning for apply passport and afternoon for take back the passport).
My friend 's agent said that she will keep maid's passport for employer's safey sake. 1. They cannot borrow money. 2. They cannot find another job. But the agent seems that no request the maid to write this kind of letter.