Who is Mrs. Gates from The Nine Tailors: Changes Rung on an Old Theme in Two Short Touches and Two Full Peals and what is their importance?

Mrs. Gates is employed as the housekeeper at the Red House. She is described as a snobbish and class-conscious woman, behavior that allows the police to work out when the body was put into the grave. Mrs. Gates was able to factually provide infomation as to when her own funeral wreath was set aside because she'd given direct orders that it not be moved.