In her first meeting with Dean, they asked each other questions. Dean asked about the deaths that occurred at the hospital, while Erica asked a bit about Dean's past.
She referred to Dean as a "paranoid schizophrenic with narcissistic personality disorder and religious psychosis", which was apparently written on his file.
When she met Dean again, she bemoaned his difficult life as a hunter who was struggling to protect the world, and made him ponder briefly about the weight on his shoulders.
After Dean missed their next session, Erica began guilt tripping him over his failure to prevent the Apocalypse, and the deaths of Jo and Ellen. Shocked by her sudden change in demeanor, Dean demanded to know who she was. Erica revealed that she is not real, and was all inside his head, because he was going crazy.
Dean found out in the end that she was a hallucination which resulted from being infected by the wraith inside the hospital.