Another thing points to Molly Spence being Bessie's niece rather than her sister. Her husband, Melville William John Spence, seems to have appeared as a witness in his own parents' divorce in November 1929 ("Townwsville Bulletin" 23 Nov 1929) and at that time his age is given as 17. This means he was born c.1912 which would put him in the same age bracket as Mary Margaret Topping, daughter of Mary Margaret O'Grady and William Topping.
Is the family relationship becoming any clearer, Carolyn, or are we just mudying the waters in your identification of Bessie's family? :)