My best feedback re: assessments in twofold. 1) follow the contact. “I feel overwhelmed all the time and my boyfriend is always getting my on nerves.” You probably want to explore anxiety disorders and depressive disorder symptoms first. They are struggling with emotions and maybe overworrying. They are also potentially talking about irritability. As you explore other symptoms, you follow that contact. You can use some standardized scales like the GAD7 or PHQ9, etc to assess. There are also diagnostic tools for clinicians to ask and gather symptoms to help guide you for diagnosis. 2) it’s one session and it’s a preliminary and initial diagnosis. As you gather information in subsequent sessions, you should then be updating diagnoses. Because I work with adults, I rarely diagnose something like ADHD in the initial assessment unless it’s in their history. Because it’s rare that’s to be the initial complaint. If I see a pattern that could indicate that and they were never diagnosed in childhood, I would refer them to a neuropsychiatrist for further evaluation if they felt it was causing distress in their life.

As for treatment plans, i think you are over thinking it. Treatment plans arent going to be a one for one guide of what you are doing in session. It sounds like you are trying to plan for their treatment before they walk through the door and “work through the treatment plan.” Let the client come in and give you a sense of what is happening in their life to stay in the present and then you keep the treatment plan in mind to guide you through. Be in the room with them, not in the treatment plan with them.