Lamb was born on 29 May 1883, as one of ten children born to parents John Augustus Robertson Sr. (1852–1924) and Jane Moore (1859–1926). She was born in a bark roof cottage on a sheep property near Hebel, Queensland, likely in the territory of New South Wales. Her paternal great-grandfather, James Robertson (1781–1868) emigrated from Scotland to New South Wales, to work as a clockkeeper. He was given 86 acres on a site now known as Cremorne Point in Sydney. Her maternal grandparents were immigrants from Ireland.

In 1910, she got married, and went on to have four children: Loraine Gillan, Enid Haley, Bernard Lamb, and Alice Lamb.

When asked about the secret of her longevity, she replied that the key is simply being happy. At the age of 105, all four of her children were alive, and she had 13 great-grandchildren and two great-great-grandchildren.

Lamb passed away at a nursing home in Mosman, New South Wales, Australia, on 25 June 1993, at the age of 110 years, 27 days.