Although her early training was in psychology and philosophy, her most prolific research engagements concerned women's social roles and how these changed after the Industrial Revolution.
For a short period of time, she worked as a domestic servant until she finally received a scholarship from the Czech government operating in exile (Lyon 2007, p. 832).
Her encouragement of women to work if they so desired, was perceived by critics as a destructive social force, provoking destabilization and family problems.
Starting in 1951, she collaborated with the Swedish sociologist Alva Myrdal and together they eventually published the book Women's Two Roles: Home and Work.
Providing a question about sources of the knowledge about womanhood and examining studies from the beginning of the 19th century, she wanted to prove that "what we think of specific perspectives are not guaranteed truths but the ideas subject to the influence of surrounding culture and personal bias" (Terrant 2006, p. 134).
She observed that scientific objective studies about femininity are full of stereotypes and repeat particular traits like "passivity, emotionally, lack of abstract interests, greater intensity of personal relationships and, an instinctive tenderness for babies" (Klein 1946, p. 164).
"Male and female roles are thought to be the new members of the social group in innumerable and subtle ways almost from birth.
Contrary to Parsons' functionalistic understanding of Role Theory and sex-roles division, Klein understood the concept more broadly, that femininity and masculinity should include also personal traits that can be more or less assigned to the opposite sex's character (Terrant 2006, p. 150), a concept later solidified in transgender and queer theory (e.g. Butler 1990; Bornstein 1995).
Within Mannheim's sociology of knowledge framework (Wikipedia outline: The sociology of knowledge is the study of the relationship between human and the social context within which it arises, and of the effects prevailing ideas have on societies) and its standpoint to understand how "individuals give meaning to their ongoing reality within context [that is] structured by specific institutions [and how] social values structure our perception, give legitimacy to certain ways of seeing the world, and give moral credence to particular patterns of relationships" (Farganias, p. 12-13) reality is understood by individuals within institutionally structured frameworks.
Concerning the social world, "Mannheim’s perspective required the thinker to look for ways of interpreting the situation more clearly and productively" (Terrant 2006).
In this context, Klein understood that women have a secondary status like particular discriminated groups in society, for example black Americans, Jews or immigrants (Terrant 2006, p. 171).
What she believed to be the most challenging for women was that they "internalized the sense of secondary status" (Klein 2006, p. 174), thus many accepted their own suppression.
Both were refugees from the Nazi regime, they first encountered each other in the London School of Economics, where Mannheim helped and guided Klein in the process of earning her second doctorate, this time in sociology.
In the preface to the second edition, Klein responds to criticism from other authors, especially sociologists who reproach her for a lack of own research and sociological studies.
The writer Rosa Macaulay, was one such critic who accused her of using "secondary sources" instead of doing "original research" (p. xv).
Klein explains that the universal theme that is the feminine role deserves to be constantly re-examined and matched with old and new studies, because scholars' ways of thinking guide our understandings of society more subjectively than objectively, regardless of the empirical framework.
Some main questions about the evolution of new women's roles and traits, structure Klein's thesis: What is the new ideal of femininity?
Comparing different research demonstrates that the scientific knowledge has directly or indirectly influenced the "general trend of intellectual and emotional development."
Some turning points began the process of emancipation of women and their roles inside the social group that they are assigned to in societies.
"Owing, presumably, to the emotional character of philanthropic work and to the absence of pecuniary profit attaching to it, it did not seem "improper" for women of standing to engage in charitable activities, and soon we find ladies of rank and consequence running charity organizations, working for prison reform, collecting rent in the slums of the East End of London, embarking on propaganda for the abolition of slavery, against cruelty to children, against alcoholism and prostitution, and for the emancipation of women.
The method was essentially questionnaires distributed by the IFUW in developed countries (USA, UK, France and Sweden).
After the industrial revolution society needs to "regenerate itself" (p. xii) perpetually, because development and progress demand that women continue in the economic sphere as they had in former times, but this takes them out of the household and into the factory or office.
Many different cultural-institutional traditions, e.g. Christianity, Islam, Communism and National Socialism, have divergent ideologies for the role(s) of women.
After the industrial revolution, the economic function shifted to companies, this fueled not working as "a high standard of living" for women to define their upper class statuses.
Psychologists and sociologists proved that women and men were not so different and if a man tended to be stronger for example, a woman was more agile.
This process had been accelerated by both the World Wars, women had a huge importance in economic capital when men were fighting on the battlefield.
The second phase of this social revolution had two major developments; "the increased average life-expectancy" and "the change of the size and structure of the family" (p. 13).
Better hygienic conditions in societies and massive increases in medical knowledge and technology led to infant mortality decreasing greatly between 1850 and 1950 coupled with longer life expectancy, with averages crossing 70 years of age whereas "one half of female population died before the age of 45" (p. 7) a hundred years before.
Nevertheless, a majority of men enjoyed using their leisure time to accomplish some work-hobbies at home, becoming an amateur painter, carpenter, etc.
One thing the authors were sure about was that the choice made by women was "strongly influenced by the role they hope to play in family" (p. 77).