Green’s Dictionary of Slang

(Aus.) a woman seen as a sex object; thus through metonymy, sexual intercourse.

c.1941		Baker Aus. Vulgarisms 7: sniggle: The act of coition. 2. The female pudend.
1945		Baker Aus. Lang. 123: Other Australianisms for girls or young women include [...] sninny, snickle, tab. [Ibid.] 197: From South Australia; snickle, a girl.
1950		‘No. 35’ Argot in G. Simes DAUS (1993).
1960		J. Iggulden Storms of Summer 9: There don’t seem as much easy sniggle in the town without Doreen.
1971		F.J. Hardy Outcasts of Foolgarah (1975) 196: But that is not his good wife on his arm. Don’t say he’s done it again, bringing some young sniggle with him on an official occasion.