Knowledge construction is an essential scientific practice, and undergraduate research experiences (UREs) provide opportunities for students to engage with this scientific practice in an authentic context. While participating in UREs, students develop conceptualizations about how science gathers, evaluates, and constructs knowledge (science epistemology) that align with scientific practice. However, there have been few studies focusing on how students' science epistemologies develop during these experiences. Through the analysis of written reflections and three research papers and by leveraging methods informed by collaborative autoethnography, we construct a case study of one student, describing the development of her science epistemology and scientific agency during her time participating in a biology education URE. Through her reflections and self-analysis, the student describes her context-dependent science epistemology, and how she discovered a new role as a critic of scientific papers. These results have implications for the use of written reflections to facilitate epistemic development during UREs and the role of classroom culture in the development of scientific agency.