Recently, K-12 engineering education has received increased attention as a pathway to building stronger foundations in math and science and introducing young people to the profession. However, the National Academy of Engineering found that many K-12 engineering programs focus heavily on engineering design and science and math learning while minimizing the development of engineering habits of mind. This narrowly-focused engineering activity can leave young people--and in particular, girls--with a limited view of the profession. This study describes Digital Zoo, an engineering learning environment that engaged girls in authentic engineering activity in order to link the development of engineering skills and knowledge to engineering ways of thinking. Specific activities from an engineering practicum were recreated in the learning environment, where ten middle school girls from diverse backgrounds role-played as engineers designing solutions to a client-based project. Responses on pre, post, and follow up interviews suggest the participants were able to develop each of the five epistemic frame elements--engineering skills, knowledge, identity, values, and epistemology--as a result of Digital Zoo. In situ data from the intervention was analyzed with a sophisticated mixed methods approach that integrated qualitative methods with a new quantification technique, Epistemic Network Analysis. These techniques allowed for the exploration of complex thinking and learning throughout the different activities of Digital Zoo. The results of this analysis identified client-focused activity and notebook-based reflection as two activities within Digital Zoo that fostered key linkages to engineering values and epistemology.