It depends on what you want to do within the psych field. Are you interested in just doing therapy? Then just get a master's in social work or counseling. Do you want to do research, teach, AND practice? Then a PhD or PsyD might be the better route. However, if you are already an RN then I'd say a psych NP is pretty lucrative and wont take nearly as long to prepare for. Going back to be a psych NP will take you 2 years of a master's. Going back for a master's in counseling or social work might take 2 years but you wont have the benefit of being able to prescribe medication. To get your psychology degree, you'd have to probably get a post bac and do research in a psych lab to gain experience during that time (2 years), apply for programs (1 year), and then get the doctorate (5-6). That is A LOT of time compared to other options and would only be advisable if you really wanted to do research, conduct assessments, and go into academia. If all you want is to be able to practice therapy, there are faster routes.