Can you provide a better explanation? I'm not sure what detectivecore is since there's a lot of interpretations, from Victorian Sherlock Holmes, to Golden Age of Detective Fiction, to gritty Film Noir PIs, to kidlit, to forensic white lab coats, to mysteries solved by non-detectives like in school stories. It's also perfectly fine to just say "detectives but make it kawaii" as an aesthetic- no page necessary! The specificity and uniqueness is quite interesting, and there are less resources because of that.
Your friend might want to check out the "Blending Aesthetics" page. It is scanty, but I did write a section about "characters" with different aesthetic blends. It will take a lot of experimentation and figuring out, but that makes it individual. Also take a look at the "Helping You Find Your Aesthetics" page. The Bottom-Up approach is what your friend seems to be going for, which is so cool!
But if she does want a jumping off point, I have some ideas. There's yyxy's "Love4eva" music video; pastel and light academia; the Nancy Drew series; maybe some Classic Lolita and girly Regency and Edwardian inspiration for the antique detectives; and studyblr but for forensic notes and secrets. Also, shameless plug, but check out mine and OnlyLadyHydra's profile for "aesthetic lists." They're concepts that are written down without images, so that would make it easier to describe.