There is another possibility - a birth in 1902 in Victoria with a variation on the spelling of her given name.
WATTS Silvia Marie
Father James Salter Mother Henrietta Gertrude FARRELY
At Caulfied 1902 Reg#25081
On the electoral rolls her name is Sylvia Marie
WATTS. Her father was an architect. Sylvia is on the electoral rolls in Elsternwick to 1943 and Malvern to 1954 with occupation clerk, and if she is the wife of Wm L, at Main road, Emerald until 1977 and in 1980 Belgrave-Gembrook Road, Clematis.
Thos
WATTS, architect - mention of James Salter
WATTS.
http://www.rootschat.com/links/0olh/Parents marriage in Western Australia
WATTS James Salter
FARRELLY Henrietta Gertrude
District Perth 1896 Reg#775
Deaths
WATTS James Salter
Father Thomas Mother Martha SALTER
At Malvern 84 years 1951 Reg#4266
WATTS Henrietta Gertrude
Father FARRELLY Terence Mother Caroline GRESWELL
At East St Kilda 85 years 1950 Reg#341
The deaths of Sylvia's siblings
WALKER Sheila Mary [born Caulfied 1904]
Father Watts James Sa Mother Henrietta G FARRELLY
At Olinda 54 years 1958 Reg#4508
PALLAS Mary Genesta [Born Western Australia 1897]
Father Watts James Sa Mother Henrietta G FARRELLY
At Caulfied 64 years 1962 Reg#5632
Sylvia Marie
NASH had a will lodged for probate
http://scvprobate.com.au/probate/Search/ApplicationIndex.aspxCando