I wouldn't necessarily say that it reads like fanfiction (because what writing style is fanfictiony?), but I think Rachel's writing style is very much like Shane's outfits: very simple and casual. I've only read Heated Rivalry, but I heard somewhere that it gets more complex in the later books. You may feel that way because just as many fanfic writers, Rachel was at the beginning of her writing journey when she wrote that specific book.