By far Nadia's most favorite saying is "Ginger is a genius". Ginger is Nadia's dog, and, until she meets "The Souls", her only true friend. Nadia repeats the saying "Ginger is a genius" at least four times in Chapter 9 alone, a few times in Chapter 2, and in several random instances in other places throughout the book.
Another of Nadia's favorite sayings is "He (or she) needs a lift". It is a phrase which is actually used by her father first, when he is discussing the turtles that need to get to the Sargasso Sea in Chapter 2. Nadia uses the saying, with some minor variations, frequently later in the book when referring to Mrs. Olinski, and how the "Souls" want to help her regain her confidence.