Well, if Christine Harris were to write horror novels about 'foreign devils', she might use the concept to play on cultural differences and the fear they can generate. In horror, the unknown is often a powerful tool. So, the 'foreign devils' could be presented as beings with their own set of values, traditions, and powers that are not only different but also menacing to the protagonists. Their appearance, language, and actions might all be designed to create a sense of dread. But again, this is all speculation as there is no evidence yet that she has written such novels.
If Christine Harris had horror novels related to 'foreign devils', perhaps there would be a sense of mystery and unease created around the foreign elements. The 'foreign devils' could be depicted as having strange powers or behaviors that are different from the norm in the story's setting. There might also be a build - up of tension as the characters in the novel try to understand or deal with these 'foreign devils'. However, as mentioned before, we don't actually know if such novels exist.
Since we're not sure if she has such novels, it's difficult to define characteristics. But if she did, there might be elements of the unknown and fear associated with the unfamiliar culture that the term 'foreign devil' implies.