Establishing trust is an important aspect of the design of technological tools for mental health, as individuals are persuaded to disclose personal distressing experiences when privacy is ensured. This work-in-progress paper presents an interdisciplinary research project aiming to compare the behavior of individuals expressing trauma-related thoughts and feelings in response to trauma-evoking video clips, following three different interaction sources: a) a psychologist, b) a technological tool utilizing a human-like agent and c) a technological tool utilizing a machine-like agent. Electro-physiological, subjective and behavioral measures will be collected and triangulated to test the effectiveness of each interaction source. The design of the digital interface is presented in this paper aiming to provide insights for establishing trust in eHealth applications.