I suspect that the later identity (Vilda Henwood) would be entirely fictitous and the earlier one the real identity. My reasoning:
First, Lillian had no discernable reason to lie when she was first married, but a person hiding an act of bigamy so they could be married (and to avoid prosecution) would have reason to lie about every detail to avoid any chance of being discovered.
Second, a 36 year old Vilda passing herself off as being 26 years old seems more believable than 11 year old Lillian passing herself off as 21.
Third, the image of the Vilda Henwood marriage certificate you have posted on Ancestry gives birth as Toronto, CANADA (not Australia) - if you are making up an identity, making yourself foreign born, with both parents deceased is a convenient way to avoid anyone looking into your past. Also if the details Vilda gave are accurate there would probably be more of a paper trail - at least a 1901 Census entry in Canada, as well as a birth registration, and names on passenger lists or immigration documents somewhere.
Fourth, on a quick search I cannot find any records of a Vilda M. Henwood prior to the 1926 marriage - she seems to appear out of nowhere.
I also looked up the residence given for Vilda on the marriage certificate: 131 St. John's Rd., Glebe, in the Sand's Directory. In 1925 and earlier years that house was in the name of a Mrs. Beatrice Gough. in 1926 when Vilda was married the house was not listed, and in 1927 and later the house was in the name of C. Gilbert.
With that said, the marriage record already cited and the death record 26367/1953 agree on Vilda's parents names as William Henry and Ellen. It would be interesting to see the death record for Lilian (Harris) Chapman that reputedly died the same day at Camperdown, Victoria.