Nimmo was a vegetarian but became vegan in 1931 after witnessing a mother cow and her calf on opposite sides of a road, separated by fencing.[4] In 1948, Nimmo and Rubin Abramowitz formed the first vegan organization in the United States known as the U.S. Vegan Society in Oceano, California.[4][5][6] The Society lasted from 1948 to 1960 and was a predecessor to the American Vegan Society.[7] Nimmo distributed copies of the UK's The Vegan Society magazine and corresponded with Freya Dinshah and H. Jay Dinshah.[4] She joined the American Vegan Society and was its first paid member.[4] She authored articles for the American Vegan Society magazine, which at that time was called Ahimsa.[4]
Nimmo cared for animals in Oceano and was made an honorary lifetime member of the Humane Society.[3]