[7] Her earliest work dates from the 1890s; in 1893, a cartoon for one of her stained glass windows was shown in the Women's Building at the World's Columbian Exposition in Chicago.
[9][10][11] Armstrong's solo work—which the New York Times termed "exceptional"—included stained glass window designs for dozens of churches and chapels, as well as a government building and several private residences.
[12] One of her windows for St. Andrew's Dune Church in Southampton, New York, was blown out by the Great New England Hurricane of 1938 and found intact afterwards half a mile away.
[15] Amstrong and her sister Margaret illustrated several books together, including Max Müller's 1906 Memories: A Story of German Love.
[16] The Metropolitan Museum in New York holds a collection of her drawings and watercolors for stained glass windows as well as designs for an altarpiece and a mural.