Aaron Isaacs’s incredibly detailed book Twin Ports by Trolley gives a little more context to the mystery photo. On page 61, the caption of a streetcar employee’s portrait reads:

In an age of physical labor in a blue-collar city, motormen and conductors may not have been paid well, but as the public face of DSR [Duluth Street Railway] they were well-dressed, enjoyed a clean working environment, and from those things derived a certain social status. It is reflected in portraits such as this by professional photographers, which would not have been made of common laborers.
The author also includes the first photo that Gina posted of female conductors (called trainwomen or conductresses at the time) and devotes pages 79 – 82 to their history. He notes that 21 women were hired as conductors starting from May 10, 1918 (during the last year of the World War I). They were not let go when the war ended and the veterans returned home. Specifically, 18 of the women remained on the job in 1922. By 1924, the number was down to five. 

The one woman in the 1929 photo posted by Gina must be either Christine Pearson or Elizabeth Cook, as Isaacs references an August 1928 story in the Duluth News Tribune that features interviews with these last two women working on the streetcars, describing how much they enjoyed their work and their plans to stay. The photo must have been taken shortly before this woman lost her job, as the DSR had laid off both women by May of 1929 after the company moved from two to one person operation on a large number of streetcars.