My honest opinion after reading your story is that you gave up on law school because the curriculum format was difficult and it turned you off. Anyways, you are thinking on the right track to writing your PS. I wouldn't say anything negative about law school in your paper, and make sure you avoid any implications of it too. Who knows who might read your paper; it could be a pharmacy law professor.
I would mention law school but don't go into a list of "why law school wasn't for me." Instead, talk about your pharmacy experience and what you love about it and what you take away from these experiences.