Isobel Louise Sophie Guthrie was born in Cape Town in 1879. She was the daughter of English-born botanist and mathematics professor Francis Guthrie and his wife, Isabella Grisbrook.
In the beginning of 1918, she was a botanical assistant at the Bolus Herbarium until 1927. While there, she developed her skill as a botanical illustrator and is best known for her series of 264 depictions of protea species found in South Africa which she begun in 1925, with the last dated in 1947. She donated the set to Bolus Herbarium in 1948. The Guthrie plant was named in honour of Louise.
Her art is archived at the University of Cape Town while some of her watercolours are on display at South Africa House in London. The Hermanus Botanical Society held an exhibit of 76 paintings by Guthrie in 2000 at the Fernkloof Nature Reserve.