Madame was pronounced dead prior to Justine's birth. A hidden note in the Crypt states "You see, his wife had died while giving birth to his son". This implies that Justine could have had a brother, or she is transgender.
The statue in the Crypt was used as a monument to her for where she was buried.
This same statue was later intended to be used in the main game, in the area of the Cells, where Daniel would awaken in the Crypt, and this specific statue would be a monument to Alexander's "love".