Bertram Shaw's mother.

Emily shared her home with a man named Bertram Shaw and passed as his wife. Shortly after eleven o’clock on the morning of 12th September an elderly lady called at the house in St Paul’s Road. This was Mrs Shaw. She had travelled from the Midlands to visit her son who, she understood, had recently married. Mrs Stocks, the landlady, told her that her son’s wife was still in bed. They talked together in the hallway for about fifteen minutes until Bertram Shaw returned from work. He was employed as a dining-car attendant on the Midland Railway whose main lines ran to Leicester, Nottingham and Sheffield. His hours of work enabled him to catch the seven-twenty a.m. train from Sheffield to St Pancras and to reach his home shortly before eleven-thirty.
After exchanging a few words with his mother and the landlady Shaw went to call Emily. Receiving no answer when he knocked at the door he tried to open it and found that it was locked. He went to the kitchen and borrowed a duplicate key from Mrs Stocks who followed him into the parlour. Evidence of an intruder was all over the room. Drawers had been ransacked and their contents strewn over the floor. The folding doors leading to the bedroom were also locked and the key was missing. Again Shaw knocked and, receiving no answer, broke into the room. The blankets were in a heap on the floor. The sheets covered something on the bed from which a pool of blood had trickled down on to the floor. The room was dimly lighted through half-opened shutters.
Shaw, thoroughly alarmed, rushed to the bed and dragged aside the sheets. To his horror he discovered the nude body of Emily Dimmock lying face downwards. Her throat had been cut from ear to ear. The Mammoth Book of Unsolved Crimes. Roger Wilkes.
 This is the first reference to Mrs Shaw. Bert's mother wasn't there. I suggest the reason the author used  Bert's mother was to add drama and to confirm that Emily Dimmock was a slapper, who didn't regularly perform domestic duties. She was hastily slaving over a hot copper only because she about to encounter her future mother-in-law.

And where did the name Robert Roberts come from? It's Thomas Percival Roberts. Names and stories are repeated from one article to another as if chiselled on granite.