In her lifetime, Cowper's photographs were widely circulated as illustrations in South Kensington Museum publications and examples of her work are continually being discovered in libraries and archives around the world.

In 1841, Henry Cole, the founding Director of the South Kensington Museum, and an advocate of wood-engraving as a suitable career for women, employed Cowper and her sisters to engrave the illustrations to his guides to Westminster Abbey[9] and Hampton Court Palace.

[8][10][11] Cowper made numerous wood engravings for a range of publications, including Cole's guidebooks, the 19th century English writer and art critic John Ruskin's fairytale, The King of the Golden River, written for twelve-year old Euphemia (Effie) Gray,[12] and a collection of children's stories compiled by illustrator Richard Doyle.

[14] On 30 March 1852 Isabel married Charles Cowper and moved to 4 Campden Hill Terrace in Kensington.

Cowper's negatives were put to work in a variety of manner: they were used to print albumen positives; employed in photomechanical processes producing illustrations for the volumes published by the museum that were widely circulated to the regional art schools and galleries as well as to international museums and libraries; they were collected in the National Art Library for use by artists and scholars; they were sold to the public at a dedicated sales stall located onsite at the museum; they were used as models for the still life examinations that were part of the National Curriculum; and they were also made into lantern slides which were employed by museum experts as projected visual examples for instructional lectures.

[31][32] Cowper also exhibited photographic works in the International Fairs of 1871,[33] 1872,[34]1873[35] and 1874[36] for which she was recognised in the art press.

When first employed, Cowper was paid at a rate of 3 pence per square inch of glass negative made.

As a woman, Cowper was denied a position within the civil service, among whose ranks most male members of the museum staff were employed.

[42] With the death of Richard in 1908, Cowper moved to Glasgow, Scotland, residing at 9 Derby Crescent, joining her married daughter, Beatrice Hedley.