I have read most of the discussion on Catherine being a heroine as the narrator explaining why, if we were expecting to be reading a horrid novel, the main female character does not seem to fit the mold.

I also get the impression that though she may have done a lot of novel reading it is Isabella who is pushing her towards the horrids. And since I just read up on circulating libraries, it is possible that Catherine only read the meager selection of novels available in her village and is now ready to branch out into the myriad of horrids available in Bath.