The book is a chapter book, probably about elementary school reading level? Along the lines of goosebumps. I think I remember black and white illustrations scattered throughout the book, but not more than four or five I think. I remember some of the details pretty vividly because it was a very weird book, but I can’t remember the name and google searches for it just sort of turn into word salad.
The main character is a girl who expresses a fear of almost everything (I remember that alien abduction is specifically mentioned as a reason she doesn’t want to go outside?). Her name was Katie or Emma or some other names that can have a lot of different nicknames. Her family goes to a mall where a mysterious/creepy Easter Bunny mascot gives her younger brother a plush Easter bunny, which he loves and she despises. The girl begins to hear “thumping” in the hallway and finds the plush in odd places, leading her to believe that the plush is alive and malevolent. Unrelated to the rabbit, there is a scene where she participates in a class play about the myth of Hades and Persephone and hallucinates that she sees the myth occurring out the window of the classroom.
The back half of the book is fuzzier for me. On Easter night (or the night before?), her brother goes missing (presumably kidnapped by the plush) and she has to go down a rabbit hole in her backyard(?) to follow the plush rabbit and save her brother. Somewhere along the way she finds a table setting with name cards that are all variations of her name, but none of them are the nickname she prefers and I think it’s probably symbolic of something? At some point in this journey she ends up on the moon. I think she has to make a declaration about how she will be brave and face her fears in order for the bunny/the universe (???) to give her brother back to her? I think the lesson learned was that you shouldn’t be scared of the unknown.
The blurb on the back of the book seemed to give me the impression that it was part of a holiday themed children’s horror series, but I don’t recall ever seeing anything that looked like it was from the same series