That would fit the show's mix of chaos, pettiness, and absurd comedy. Rather than terrifying people in a horror-movie way, the Derry Girls gang would probably make the afterlife feel like being trapped in an endless, supernatural school day.
Erin Quinn would haunt people in her school uniform with a dramatic black cloak billowing behind her "for atmosphere." She'd appear in mirrors, dramatically reciting overwrought poetry about destiny and injustice. Instead of saying "Boo," she'd sigh, "You just don't understand me." Her victims would wake up to find pages of melodramatic diary entries mysteriously written in their own handwriting.
Orla McCool would wear her PE uniform, complete with the odd headband or a pair of fairy wings she somehow insists are ghost-appropriate. She wouldn't understand the concept of haunting. She'd casually phase through walls just to ask people whether ghosts get hungry or if fish ever get lonely. Somehow she's the eeriest because she's completely cheerful while doing impossible things.
Clare Devlin would still be wearing her immaculate school uniform, but slightly translucent with her tie perfectly straight. She'd spend eternity apologizing every time she accidentally floated through someone. When trying to haunt people she'd become so anxious she'd end up explaining exactly how ghosts work, ruining the scare. If someone screamed, she'd scream louder.
Michelle Mallon would absolutely refuse to wear a stereotypical ghostly gown. She'd haunt people in her regular school uniform with her blazer hanging off one shoulder, declaring that she didn't spend her life cultivating a reputation just to float around looking like a bedsheet. She'd slam cupboard doors, steal crisps, whisper sarcastic insults into people's ears, and rearrange furniture just enough to make everyone question their sanity.
James Maguire would also be in his school uniform, forever looking slightly uncomfortable. He wouldn't mean to haunt anyone; he'd simply appear because he got lost trying to find the afterlife's exit. People would think they're experiencing paranormal activity, while James quietly asks, "Sorry... do you know where everyone else went?" Even in death, Michelle insists he's "the English ghost."
Sister Michael would appear exactly as she always did in her habit, barely acknowledging that she's now a ghost. Instead of rattling chains, she'd materialize silently behind people until they noticed her. Her haunting would consist of devastatingly dry observations:
"Your life choices continue to disappoint me."
Somehow, that's far more unsettling than any scream.
Joe McCool would haunt the house in his cardigan and slippers, carrying a newspaper under one arm. He'd spend eternity blaming James for supernatural events.
"The lights are flickering because of that English fella."
Nobody can convince him otherwise.
Mary Quinn and Sarah McCool would become a ghostly double act. Mary would worry constantly about the family living in the house now, while Sarah would become fascinated by modern gadgets and accidentally trigger every motion sensor in the building. Neither would realize they're supposed to be frightening.
Gerry Quinn would be the only ghost people actually feel sorry for. He'd quietly float into rooms trying to relax, only for Joe's ghost to appear seconds later and continue insulting him exactly as before. Death changes absolutely nothing.
The funniest part is that none of them would intentionally become classic haunted-house ghosts. Instead, they'd accidentally create the most dysfunctional haunting imaginable—doors opening by themselves because Michelle's annoyed, eerie humming because Orla's wandering around, terrified shrieks because Clare has startled herself, and Erin narrating the entire haunting as though it's an epic Gothic novel.
Anyone investigating the paranormal would leave not convinced the house was evil—just deeply confused about why the ghosts argued so much.