Although born in Chicago in 1883, Margaret moved to Idaho at the age of six when her father, Calvin Cobb, bought the Idaho Statesman. Margaret was raised a socialite and went to Miss Porter's Boarding School in Farmington, Connecticut. She also travelled abroad to France in World War I as a member of the Red Cross. She returned to Idaho at the age of 36, in 1919. After her father died in 1928, she took over her father's duties and remained the publisher of the Idaho Statesman until 1959.

Margaret was the first female publisher for the Idaho Statesman. In 1942, she led the Statesman to produce and evening paper, and led the paper to reach a circulation goal of 50,000 for the Sunday edition. The newspaper achieved a daily circulation of 30,000 in the early 1940s under her leadership and became one of the premier newspapers in the Northwest.

In addition to following her father's footsteps with the newspaper, Margaret also continued his civil campaigns and focus on Boise. Her father had campaigned for civic improvements to Boise, and the Statesman is credited with bringing the telegraph and telephone to Boise as well as the Union Pacific Railroad. Margaret supported many civic enterprises and contributed to numerous Boise charitable, religious, and educational organizations. She also often supported and attended the annual Boise Basque Ball held during the holiday season.

Margaret was a driving force behind the construction of Bronco Stadium at Boise Junior College (now Boise State University). The Statesman, under Margaret's direction, advanced almost the entire cost of building the stadium. Another project Margaret felt deeply about was the restoration of pioneer cabins and early vehicles on display in Julia Davis Park. Margaret planned and supervised the restoration of the buildings and vehicles. Near the end of her life, she incorporated the Margaret Cobb Ailshie Trust, with the hope of creating a perpetual source of funding for Boise charities and educational institutions. The first distribution of funds from her trust was made in 1961, providing $25,000 to Idaho hospitals, orphanages, colleges, and the Boise chapter of the American Red Cross.