Millicent Franks was appointed in November 1901 (at the age of 15) as botanical artist and assistant to J.M. Wood* at the Natal Herbarium in Durban. In 1903, when Frieda Lauth* left the herbarium, she became chief botanical artist. She did most of the illustrations for Volumes 3 to 6 of Wood's Natal plants, the last volume of which was published in 1912. She also contributed some illustrations to H.W.R. Marloth's* Flora of South Africa (1913-1932). Her collecting activities produced some 370 specimens from Van Reenen, Camperdown and Durban, most of which went to the Natal Herbarium and the National Herbarium in Pretoria.
In September 1910 Franks was elected a member of the first council of the (short-lived) Natal Scientific Society. As co-author with J.M. Wood she contributed a paper on "Kaempferia natalensis Schltr and Schum", which was published in the society's journal The Naturalist (1911, Vol. 1(3), pp. 112-115).
Franks emigrated to England in November 1914 and spent three months at Kew Gardens working on illustrations for Wood. In 1915 she married Howard Flanders. She was commemorated in the species names Celtis franksiae, Brachystelma franksiae and Euphorbia franksiae, named after her by N.E. Brown*, and Ischaemum franksiae, named by J.M. Wood.