Isla trained as a botanical illustrator under the tutelage of a fellow of the Linnean Society, subsequently developing a personal style that sits between scientific record and fine art object. She works in watercolour, gouache, and pencil on heavyweight hot-press paper, often spending weeks on a single plate. Her subjects range from common British wildflowers to endangered plant species she documents in collaboration with botanic gardens. Isla's illustrations have been published in several natural history books and she exhibits regularly at the Royal Botanic Garden Edinburgh and other institutions across Scotland.