I'm looking for a book that I read in 3rd grade. It was about a girl whose neighbor was an odd woman. The girl believes the woman is a witch because she people in the neighborhood disappear and the woman has many many cats, each with a name that are the missing neighbor's initials (e.g. CJ). That is unfortunately all I can remember about this book, and it's been driving me crazy trying to find it! Please help!
This sounds like "No Such Thing as a Witch" by Ruth Chew. Here is an excerpt from her summary:
Nora and Tad are given fudge by a neighbor named Maggie Brown who has a lot of pets. After her brother and father start acting strangely, she deduces that one piece of fudge makes you like animals and that two lets you understand what they say. Mrs. Cooper gets angry when Tad and Mr. Cooper start feeding Skipper people food, and Nora goes over to complain to Maggie, who explains that the fudge wears off after a while. Nora and Tad visit Maggie again and pretend to each eat one piece of fudge. They each also take an extra piece. When they get it home, Tad eats two pieces, then three, starts acting a bit like a cat, then takes Nora's, and turns into a cat.
You can read some of the book on Google Books here and see if it matches what you remember.
Some details sound like it could be "The Cat Sitter Mystery" by Carol Adorjan.
WHAT WAS HIDING IN THE MANSION NEXT DOOR?
There was something scary about the house next door. Beth certainly didn't believe in ghosts, but the big old mansion set in the shadows did look haunted. Even Mrs. Goodall, the owner, looked a little like a witch, with bright red hair that was green at the roots. But she had lots of cats, and Beth loved cats.
But when Beth agreed to take care of the cats while Mrs. Goodall was away, all kinds of strange things began to happen. Every time she went over to feed the cats she heard creaking noises coming from different parts of the house ...doors opened and closed by themselves...and lights mysteriously went on and off. Something beside the cats was lurking in the house next door!
"Mrs. Goodall's a witch," Tiffany Tanner said.
..."What makes you think she's a witch?"
"She has a black cat, doesn't she?"
"Lots of people have black cats, Tiffany."
"Maybe they're all witches," Tiffany said.
Cats' names are initials:
O.C., F.C., C.C., L.C. Such strange names for cats. Like people's initials. Suppose they were people's initials. Suppose Tiffany was right. B.C., Beth thought. Beth Carew.
How much more exciting it would have been if Mrs. Goodall were a witch! If someone were imprisoned in the attic, or if the cats were not cats at all, but people under a spell,...
You can read it on archive.org.