McArthur was a strong environmentalist and a co-founder, with Judith Wright, David Fleay and Brian Clouston, of the Wildlife Preservation Society of Queensland in 1962, and served as vice-president from then until 1965. In 1963 she founded the Caloundra branch of the society.

She was involved in several campaigns during the 1960s and 1970s to preserve landscapes threatened by economic development, including the Pumicestone Passage, the Great Barrier Reef and Cooloola. Much campaign work was funded through her growing and selling native plants as well as through exhibitions of her wildflower paintings. She was especially concerned for the Wallum country of south-eastern Queensland, a habitat characterised by floristically-rich coastal heath and swamps on deep sandy soils.

The spider, Ozicrypta mcarthurae, was named after her for her outstanding contribution to conservation. In 1966 she was awarded and Honorary Doctorate By James Cook University of North Queensland.

McArthur wrote a weekly column, Wildlife and Landscape, for her local paper. She also started the Lunch Hour Theatre in Caloundra, a monthly event for which she wrote scripts based on environmental, biographical and historical subjects. Books authored (and illustrated) by McArthur include:

• 1959 — Queensland Wildflowers — A Selection. Jacaranda Press: Brisbane.
• 1978 — Pumicestone Passage: A Living Waterway. Bacchus Printing: Brisbane.
• 1981 — Bread and Dripping Days: An Australian Growing Up in the 20s. Kangaroo Press: Kenthurst.
• 1982 — The Bush in Bloom: A Wildflower Artist’s Year in Paintings and Words. Kangaroo Press: Kenthurst.
• 1985 — The Little Fishes of Pumicestone Passage. Artworks: Brisbane.
• 1986 — Looking at Australian Wildflowers. Kangaroo Press: Kenthurst.
• 1989 — Living on the Coast. Kangaroo Press: Kenthurst.