Poussey's death is a fictional element in the show. It's part of the creative storyline and not based on any real-life incident. The writers crafted this for dramatic effect and to drive the narrative forward.
Overall, Orange Is the New Black is moderately fictional. It combines elements of real prison life with fictional characters and plotlines to make it more entertaining. Some aspects are exaggerated for effect, but it still offers insights into prison dynamics.
I don't know. Maybe there are elements inspired by real events, but it might not be a straightforward account of a true story. Maybe look for interviews or behind-the-scenes info to get a better idea.