She was cast as leading lady in Smart Money in 1931, the only film starring both Edward G. Robinson and James Cagney.

In 1932, Knapp was one of 14 girls, along with Ginger Rogers and Gloria Stuart, selected as WAMPAS Baby Stars.

In 1943, she played her last role, uncredited, in Two Weeks to Live, one of the Lum and Abner films starring Chester Lauck and Norris Goff.

In 1931, Knapp spent several months in the hospital[3] after she fell from a cliff during a hike with her brother, Orville.

[5] On June 9, 1981, Knapp died of heart disease at St. Vincent's Hospital in Los Angeles, California.