A theme of the book that Mildred's actions support is mass media.
What is the theme?
In the book, Fahrenheit 451 by Ray Bradbury, the theme of Mass Media is a prevalent one. There was a form of censorship in society and television was a tool used by the government to draw people away from one another.
Mildred had developed a strong attachment to the television and that was why when the fire burned her home, she was more concerned about the television family than losing Montag. This was a reflection of the extent to which she was censored. So, the theme is mass media.