This was really fun! I think it balanced having horror elements and being appropriate for middle grade audiences really well. I, an adult, felt tense at some moments (this may be mostly because i have a phobia of blood and needles though lol). I can see it being a good intro-to-horror book for some kids. 
Also i love to see stories about young fat girls going on adventures! The book is good fat rep and has some really sweet moments with Maggie gaining confidence in herself.
I’d definitely recommend this book to some of the kids in my life, as well as any adults who want to explore middle grade more