Armstrong was the artistic director of Armstrong Chamber Concerts, a non-profit organization she founded to bring musical education to public and private schools. More than 100,000 students participated in the program in Connecticut's Litchfield and Fairfield counties, Harlem, and the Bronx. Armstrong developed ACC's reputation with a roster of more than 100 established artists.

Over the past few decades, Armstrong performed on her 1760 Guadagnini in private homes in Greenwich and in other venues in Washington and New Milford, as well as at Carnegie Hall. She also built a reputation as a teacher.

Armstrong was a graduate of Juilliard, where she studied with Dorothy DeLay and Ivan Galamian. She made her Lincoln Center debut in 1976 and performed with orchestras including the Boston Pops and the Indianapolis Symphony, and with the Martha Graham Dance Company.

Armstrong recorded on the Musical Heritage, Elysium and CRS labels.

She died unexpectedly of natural causes, according to the News Times.