I also have 2 rooms only, one is for myself, one is the study room, it is not enough room to set up a bed for her there, so before I told the agent beforehand that I can only provide a sofa bed(open at night and close in the day) for her. Different agents say different things, one said she must have a fix bed, one said that as long as there is privacy for her, it is OK. Anyway I told the agent about this and make sure she knows this before she comes to HK.
I also have a friend who let her maid sleep in lounge, but she managed to set up a curtain to make some privacy for her and her maid slept like this for two years until they moved to a bigger place.