In the novel The Mirror Crack'd from Side to Side a character named Bianca makes a brief appearance in Chapter 18. She was awakened in the middle of the night by what sounded like a gunshot. She was almost sure she had heard a shot but then decided that she had been mistaken and so went back to sleep.
It is not exactly clear who she is, but given the circumstances, she must have been sleeping at Gossington Hall, and probably near the room of Giuseppe who was the one being shot at this point in the story. Since the servants rooms would have been close to one another, this makes it possible that Bianca is a maid in service at the mansion.