I totally get why someone would want more like 'Sadie'. That kind of raw, investigative podcast framing mixed with a girl's brutal quest is so specific. For a lead with that same relentless, damaged drive, try 'The Girl with the Dragon Tattoo'. Lisbeth Salander is in a league of her own—brilliant, deeply traumatized, and utterly uncompromising in her pursuit of justice against men who hurt women. The plot is a much slower, colder burn than 'Sadie', more of a corporate conspiracy thriller, but the core of a woman using her particular skills to hunt predators is powerfully similar.
Another angle is the audiobook presentation. 'Sadie' uses the podcast format so well. 'Illuminae' does something comparable with its found-document style (emails, files, chat logs), though it's sci-fi. For a purely psychological thriller with a complex female perspective spiraling into an investigation, Gillian Flynn's 'Sharp Objects' is brutal and brilliant. The protagonist, Camille, is a journalist returning to her hometown, and her voice is just as hauntingly broken as Sadie's, driven by a need to uncover truths that are deeply personal and painful.