I don't think it's certain that Julia CURTIS who died in 1917 is the same Julia CURTIS who arrived in 1857 although it's possible.
However I believe that there's reasonable evidence to show that the father of at least some of the children of the Julia CURTIS living in Prahran in the 1860s was most likely to be Thomas Elder BOYD.
See Reply #31 which shows someone called Thomas CURTIS was living in the same street as Julia at the time of the birth and death of Julia's baby in 1866/7
Reply #36 where Thomas CURTIS is recorded as Thomas Boyd CURTIS.
Reply #37 Thomas BOYD is a witness at the marriage of Julia Laura
Reply #46 has a comparison of the signatures of Thomas Elder BOYD (the younger) when he signed the application for probate of his father's will in 1860, and a signature of a Thomas BOYD as a witness, on the marriage certificate of Julia Laura CURTIS 1888, daughter of Julia CURTIS.
Seems to me that these signatures are from the same person (with the obvious missing middle name in the second signature).
Reply #52 - Sue has made a case for Thomas CURTIS and Thomas Elder BOYD being the same person.
However, it's all speculation and the definitive truth will probably never be known. (DNA testing??

)
Judith