Seems to me that this would be one of the best possible places to start.
file:///C:/Users/Karl/Downloads/moppel_informaatika_2018.pdf
ELIZA: a very basic Rogerian psychotherapist chatbot
Something like the above in action… Eliza, a chatbot therapist
In therapy, different systems could be utilized in a chatbot format, Gestalt, REBT, or CBT, actually I could see Reflective Listening as a possibility as well. I think the therapies that are processes, that do not have goals, would be better for a bot. Gestalt and Reflective Listening and basic Socratic Questioning.