In Letter 9, Jane writes that My father is now reading the 'Midnight Bell'.

The notes say that it is a German story, founded on incidents in real life.

This book is in the list drawn up by Isabella Thorpe, to read;
CH6:
“I will read you their names directly; here they are, in my pocketbook. Castle of Wolfenbach, Clermont, Mysterious Warnings, Necromancer of the Black Forest, Midnight Bell, Orphan of the Rhine, and Horrid Mysteries. Those will last us some time.”

If Jane's father read this book then it definitely isn't a 'bad' book as one is prone to think, just because it is in Isabella's list.

It is commonly thought that Isabella was a bad influence on Catherine Morland because of the kind of books she was encouraging her to read.

So it isn't that after all!!!