I don't know who the author of 'the junkyard horror novel' is. There are so many horror novels out there, and without more information, it's hard to say.
Well, it could be about a series of murders that take place in the junkyard. The killer might be using the junkyard as a dumping ground for the bodies or using the various junk items as weapons or tools for his evil deeds. The protagonist could be someone who stumbles upon this horror while exploring the junkyard.
The 'junkyard girl' in 'Pulp Fiction' could be a symbol of the grittiness and the forgotten elements of the world shown in the movie. The junkyard itself is a place of discarded things, and if there's a girl associated with it, she might represent those who are on the fringes, overlooked or part of the criminal underbelly that the movie often explores.
The junkyard dog might be sad because it lives in a junkyard. It could be lonely, with only scraps and old cars around. Maybe it was once a pet but got abandoned there. It has to fend for itself, looking for food among the junk, and is often feared by people who pass by, without understanding its real situation.
One reason could be abandonment. Maybe its owner didn't want it anymore and left it in the junkyard. Another is lack of proper care. In the junkyard, there's no one to give it regular meals or medical attention. Also, the environment is harsh. The dog has to deal with all kinds of dangerous and dirty things.
I'm not sure if there is an explicitly named 'junkyard girl' in 'Pulp Fiction'. If there is, her role might be related to the junkyard setting which could be used as a place for illegal activities or hiding things in the movie's world of crime and chaos.
The 'Junkyard Druid' novel might have a really interesting take on the druid concept in an urban fantasy setting. It could feature a druid who has to use their skills in a very different way compared to traditional druid stories. Since it's new adult, it might also deal with themes like coming of age, finding one's place in the world, all while having magical elements related to being a druid in a junkyard - like area. There could be cool characters like other magical beings or regular humans who get caught up in the druid's adventures.