Well, PLL is mainly a fictional show, but some aspects of the overall concept might be loosely based on real - life things like high - school dramas, secrets among friends, and the idea of a mystery figure lurking around. But as for which episodes are based on a true story, that's really hard to say. Maybe the episodes that deal with cyber - bullying or relationship problems could potentially have some roots in real - life events, but there's no official statement on this.
I'm not sure exactly which PLL episodes are directly based on a true story. However, often shows draw inspiration from real - life events in more general ways. It could be that the themes of mystery, friendship, and secrets in PLL might be related to some real - life experiences people have had, but it's not easy to point out specific episodes in this regard.