The film tries to make the heroine more sympathetic. Also, it constantly makes her motives for the crimes more economic. This strengthens the film's theme of woman's economic revolt. The two screen writers can each be linked to other themes of their careers. Harry Ruskin had written many of the Dr. Kildare and Dr. Gillespie movies, as well as a few Andy Hardy pictures.
Postman seems like a medical drama at times.
There are detailed medical aftermaths to each murder attempt. The furious fights, betrayals and spectacular reconciliations of the latter half of Postman are in this tradition. However, it seems to me that the hero and heroine of Postman are basically allies. They fight with each other, but mainly they stand with each other against the world.