Playing Beatie Bow, by Ruth Park, originally published in 1980?
The main character also goes by the name Abigail. Abigail finds the dress (with a flower-crocheted neckpiece) in her mother's shop, and follows a grubby little girl around an alley or stairs around Sydney's The Rocks in the 1970s; they emerge in the girl (Beatie)'s time, the 1880s, and Abigail is accidentally injured by Beatie's father and taken in by the family. Judah is Beatie's brother, and his fiancee is Dovey (Dorcas), who has a badly healed hip.
