Not much to say about this but we’ll see what kind of padding I can come up with…
I went to the library when I was pretty young… 7 or 8 I think, and was looking for a good ghost story novel, because I had already read all the Alvin Schwartz Scary Tales books, twice, and wanted a full novel.
What I found was The Ghost at Dawn’s House, book 9 of the Baby Sitters Club. I read it…and read it again… and then started on the others. Even after I read 90% of them (she wrote hundreds…I lost interest a couple of years later), #9 remained my favorite and I read it several more times after that first time.
So, the answer to the question, which I kind of buried under everything else, was The Baby Sitters Club by Ann M. Martin.