Green’s Dictionary of Slang

a land girl; a female worker on a cattle station.

[1936		Land (Sydney) 27 Nov. : ‘Letters from Young Bees’ [...] Jillaroo of the Jungle, Gollan, 10/11/36: The wheat crops around here are nearly ripe and some of the people are stripping. I had my twelfth birthday two days before I sat for my exam].
1938		Sun (Sydney) 20 Feb. 2/5: [photo caption] Dinah Watson styles herself a ‘jillaroo’ and can throw a sheep and shear with the best of them.
1942		Dly Mercury (Mackay, Qld) 9 July 1/8: THE ‘JILLAROO’. The employment of women in the grazing industry has resulted in the coining of a new word to describe female employees on stations. [...] Mr. J. F. Meynink said women employed on New South Wales properties were known as "jillaroos.".
1945		Baker Aus. Lang. 62: The past few years have given us [...] jillaroo, a female station hand (the play is on Jack and Jill), especially used during World War No. 2 for a Land Girl.
1959		Law Instit. Journal (Queensland) XXXIII 319: Jillaroo is a phony piece of journalese which had a limited vogue during the war.
1986		J.G. Davis Seize the Wind 149: A Land-Rover had emerged from the trees, a horsewoman galloping behind who turned out to be a beefy, sweat-stained jillaroo with freckles and bouncing breasts.
1997		J. Toombs Harte’s Gold (2004) 27: Ina’s as good on a horse as any jillaroo in the Northern Territory. [...] A jillaroo is a woman who works with cattle, who looks after them.
2007		S. Griffiths Your Gap Year 423: Your chances of getting a job as a station assistant (jackaroo or jillaroo) will be improved if you have had experience with [...] farming.
2015		Guardian 4 Nov. 🌐 [photo caption] Jackaroo Malcolm Chilmon, Jilaroo Susan Gilmore and stationhand Mark Ashlin at Victoria River Downs station.