Her earliest professional training was in commercial art at the Frank Wiggins Trade School in Los Angeles. She also worked as a model for the Raymond Advertising Agency. During WWII she worked for the art department of North American Aviation where she primarily made technical drawings. At night she worked with fellow North American artist Reynold Brown on inboard drawings of aircraft used by Flying Magazine. She married Reynold Brown in 1946. In 1947 they moved to New York where Reynold pursued a career in free-lance illustration.

Reynold Brown established himself as one of the premier illustrators of movie posters before leaving the field for a fine arts career in 1970. Mary Louise was primarily concerned with raising a family and helping her husbands career during this time. Reynold suffered a stroke in 1976 and Mary Louise took on the responsibility of retraining him in his artistic skills. She continued to promote his work with exhibitions including one at Ft. Robinson, Nebraska. This resulted in a friendship with a local rancher and their eventual move to western Nebraska. She was now able to take up her own career through drawing and eventually pastels. She became enamored with the beautiful landscape of western Nebraska. She said "No two days are alike here. I'm surrounded by the beauty of the forest, fantastic sky shows and cloud buildups. I can do the same spot many times, and each time it looks different." Her "Nebraska Sketchbook" series are primarily scenes from Dawes County. These were forty pastels done rapidly on location to capture fleeting scenes as well as ten larger landscapes, also done on location but over a few days. She continues to work in western Nebraska at her home and studio in Whitney.