Dot was born to a Muggle family sometime before Frank Bryce was born. She was probably born in Little Hangleton, since she remembers seeing him when he was a child, when he showed he had a "horrible temper."
The Riddle Murders
She was one of the many town residents who gathered at The Hanged Man to gossip on the night that the Riddle family was found murdered in their home in 1943. When it was announced that Frank Bryce had been arrested, Dot said she thought Frank had always had a fierce temper, and that she had seen evidence of it when he was a child. The police later released Frank for lack of evidence, but Dot remained convinced of his guilt, remarking that he should leave, as all the villagers of Little Hangleton "knew" he had done it. In all actuality Frank Bryce was innocent, as the one who slain the Riddles that night was Tom Marvolo Riddle.