I honestly want to see more doujins emphasizing Tewi's insane longevity. She's pretty heavily implied to be the white hare of Inaba and Eirin outright says that Tewi's the one tolerating the presence of the Eientei crew in the Bamboo forest; not the other way around. Literally everything about her is massive fiction fuel, yet mangakas almost always depict her at her shallowest as an annoying trickster. What's up with that?
Yeah, it's one of the few details that I only just come across earlier. Which does goes to show how such crucial detail about Tewi is just being glossed even within the fandom (or maybe I'm just a causal fan of the franchise). It's really a shame since there's so much potential, as you said, about the amount of stories that can be spawned from this very aspect of Tewi. There seriously should a fully fledged manga about the original meeting of Kaguya & Eirin and Tewi in the bamboo forest, I've yet to see that one yet (if it is around can someone please pin my comment for it, thanks). Seriously though, it does seem that most artists simply want to display the mainstream tropes regarding her personality, as though to keep it in a sort of niche in the franchise of Touhou. Which does leave out the many paths that can be diverged into without losing the main charm of the character herself.
Hope to see more like this, or maybe find them :p