Trista

Trista is a girl and a supporting character in the series who met Greg and Rowley at the end of The Last Straw. They took her to the country club that the Jeffersons belonged to in Dog Days; within five minutes, however, she met a life guard, hung out with him for the rest of the time, and forgot all about Greg and Rowley. This causes Greg to disregard her. She has not been seen in the series ever since.

Trivia

 * Which state Trista moved from remains unknown, though in the online book, Greg notes down that Trista came from New Mexico.
 * Before The Ugly Truth was released, rumors spread that she would have a major role in the book as Greg's new girlfriend. This was however proven false when the book came out, as she wasn't seen or even mentioned.