But if you've taken all the prereqs, forget the postbacc and either focus on the MCAT or go for your NP degree. The latter will be quicker and easier, and may be the better choice depending on what you hope to do when you finish.
I will tell you that if I were an RN wanting further training, I'd go back to school to become a CRNA, especially if I were female and looking to have a family. Great lifestyle, great pay, way fewer years of training, way fewer loans, job flexibility, plenty of demand.