Who is Rosemary Kimble from Match Me If You Can and what is their importance?

Rosemary was once called Rob and was Annabelle's fiance. Rosemary appears a couple of times during the book. Once Rosemary asks for Annabelle's friendship again and another time when Kevin says something about her at a breakfast. The third time Heath goes to find Annabelle at the publishing company and runs into Rosemary.