[1][2] Brennan was born in Paris, educated in the United States and Europe and enrolled in an art school in France in 1938.

[1] In 1941 the Wakefield Bookshop gallery run by Betty Parsons included her in two shows.

[1] A book of her work, titled Skyshades: Sixty Small paintings, was published in 1990 with an introduction by Calvin Tomkins.

[1][4] Brennan's paintings are typically in miniature format and frequently combine domestic objects such as buttons with landscapes.

[5] The art critic Celia McGee said of her paintings that "Brennan's magic‐realist canvases—in which landscapes are literally put in a nutshell, a feather duster is taken to Mount Fuji, a spool of ribbon unwinds into a road, and scale and gravity are turned on their heads—are never larger than six square inches.