According to the paragraph of information given, there were no books that met the requirements for recommendation. It was suggested that he read more online novels before looking for suitable recommendations. I hope you like my recommendation.
Most likely, it isn't. Usually, such characters or stories are crafted from the imagination of the author rather than being rooted in reality. There might be some elements inspired by real-life, but it's not a direct retelling of a true story.
Chloe's character can be developed by giving her a flaw. Let's say she is overly curious and sometimes gets into trouble because of it. One time she might open a forbidden book in the library without realizing the danger, and this leads to a series of events that teach her to be more cautious while still maintaining her curious nature. As she faces the consequences of her actions, she becomes more mature and well - rounded.
I think Sabrina could be paired well with Chloe in a fanfic. Sabrina is Chloe's sidekick in the show, but in a fanfic, their relationship could evolve. For example, Sabrina could start to stand up to Chloe and this could lead to a whole new dynamic between them. Also, Luka could be paired with Chloe. Luka's calm nature could contrast with Chloe's brashness and it could make for an interesting story of how they influence each other.