In this paper, we theorize toxic white femininities as a performance and persona in school social work. To develop the theory and analytic tool of “toxic white femininities,” we used critical discourse analysis to analyze school social work professional association materials from 1906 to 1936. Our analysis isolated three performances of toxic white femininities in early 1900s school social work: (1) the exclusionary social and material gains of “her” professionalization, (2) “her” reinforcement of racial-gender-class hierarchies, and (3) “her” strategic use of helper identity to mask social control. We trace how these performances coalesced into a collective professional persona, operating beyond the scope of individual practitioners. This persona institutionalized a racialized-gendered professional identity, presented in the archives as a universal “she”—white, middle class, and feminine. With private funding from white elites in the early 20th century, school social workers—constructed discursively as white women—would become the “right” profession to shape the lives of young people and guard the privileges of whiteness. We close with a discussion of “her” long shadow and contemporary performances, outlying the ways toxic white femininities operate as a form of incremental violence impacting the profession and social services.