They do have a maid, but it was her day off. At the start of Frances' rant at Honoria in the hall, Frances says something along the lines of it was typical of Honoria to do this on the maid's day off. She used the maid's name, but I can't remember what it is.
trisher I don't think anyone would normally be let off, but we don't know what the story is yet and we're talking about Inspector Bucket here. Once he knows what happened, I can see him reasoning for himself about what to do about it. After all, he's no longer involved in the case and did say to Omid Djalili that he would discover who the murderer was for his own satisfaction (paraphrasing here!) - like a private investigator than a policeman.
It did look like she might be taking the blame though,because she thinks her husband did it (as Nelliemoser said before).