Few studies have examined how Mexican-origin mothers experience epistemic harm irrespective of its impact on childrearing. Clinicians and researchers can benefit from understanding how public narratives of (un)belonging influence the development of Mexican-origin mothers’ knowledge construction and identity as knowers. We used Chicana decolonial feminisms to examine the epistemic experiences of seven Mexican-origin mothers in the US–Mexico borderlands during a period of heightened racist, nativist, and anti-family violence. Participants between the ages of 22 and 51 years completed in-depth semi structured testimonio interviews in Spanish, English, and Spanglish, an admixture of both English and Spanish common among bilingual Americans of Mexican descent. Epistemic experiences were intertwined with crossing, bridging, and the liminality associated with navigating diverse citizenship discourses as gendered, racialized knowers. Three themes were identified including brown-on-brown conflict, discrimination denial, and co-family as sources of new knowledge. Participants experienced epistemic harm from expected and unexpected sources, including within-family invalidations that were especially disorienting. Epistemic growth arose from relational, integrated co-construction of new knowledge, but epistemic harm also appeared to cultivate internalized nativist fears in some participants.