I haven't done a lot of research into Diana Rebecca Brown however given the parents names, dates and area, I thought it a likely daughter of Mary ann.
Of course it is Mary Ann's daughter.
Births
BROWN Diana Rebecca
9 Jan 1885
Father William BROWN Mother Mary Ann THURSTON
At Avenue Range nr Kingston Wel S343/36
Death in Vic
BROWN Diana Rebecca
Father William Mother Mary Ann THURSTON
At Lillimur North 1885 4 Months Reg#2051
Cando