Mobile health seeks to provide in-the-moment support to individuals in need. In this talk, I will discuss the challenges associated with behavior and interventions that are based on language. Language is high-dimensional and complex, but is a critical component of many health and support interactions. Specifically, I will describe how we can measure empathy in mental health peer support and how we can give feedback in order to empower peer supporters to increase expressed levels of empathy, using large-scale neural transformer architectures and reinforcement learning.