Cassandra was a character in Greek myth who was destined to always tell the truth, but no one ever believed her.
The real life Glenda Cleveland never lived in the same Oxford apartment building as Jeffrey Dahmer, she lived in the adjacent building.The real next door neighbour was a woman named Pamela Bass, who is only once mentioned, by the composite fictional character named after Mrs. Cleveland.
Glenda Cleveland, who passed away on 2010, never interacted with Dahmer and wasn't present when her daughter and niece tried to alert the police about underage Laotian Konerak Sinthasomphone, but she did in fact called the police to verify what happened to Konerak and if he was a minor. The show did get right how the same police officer who returned Konerak to Damher, despite his condition, dismissed Glenda's concerns and assured her he was 19, drunk and it was just a lovers' issue.