I read this over a decade ago, probably somewhere in the early to mid 2000s. I remember it as being a fairly popular webcomic at the time, but I'm having trouble finding it now. Most of the webcomic was pretty grounded in reality, as I recall it, with the main character (a hedgehog perhaps?) managing a local theater (the only thing I remember was a male cat character who was part of a barbershop quartet that kept trying to suggest a skit about "ice cream" as per the skit from The Music Man except that I think he might have been the only member of said "quartet"). One episode (and then a running gag during the run of the comic) is that while he was visiting the local library, he met a girl who eventually revealed that she was the ghost of a girl who'd died at the library, with her disappearing when he looked away. Thereafter, it was established that she had a bit of a one-sided crush on him, and it was somewhat ambiguous as to whether she was, indeed, a ghost, or just a young girl who lived in unexplored bits of the library and had crafted an elaborate story to explain her comics and goings. I have a vague memory of her name being Nina, but I don't remember the main character's name.
Nina is something of a mystery. She's quiet and very well read. Appropriately, since she lives in the Hippedown Library. Nobody's quite sure what she is or where she's from. She insists that she isn't a ghost.
Hodges is the androgynous leader of a barbershop quartet. His (or her) voice is a rather high tenor. He (or she) is a very strict taskmaster and accepts nothing less than the best from the group. He (or she) also insists that other members not upstage him (or her), and has spent much time and many lineup changes looking for a quartet with the right combination of talent and humility.
Looking back on her introduction into the plot and the subsequent strips, I'm starting to think that I misremembered that her being a ghost was ambiguous, although the TV Tropes entry for Cute Ghost Girl agrees with me.
Unlike Minerva has Nina, the library ghost who is mildly fixated on the protagonist Brisbane. It's left ambiguous, though, as to whether she's actually a ghost or if she just grew up in the crawlspaces of the library.
This was how I found my answer, searching for
tvtropes webcomic ghost library nina.
I also misremembered Brisbane managing the theater. He lived there, but he was looking to perform as an act, with the main plotline being his business romance with Kimberly, a mercenary rabbit at the theatre. It was followed by *You Say It First, about the continued relationship after the theatre closes.