Aw, thanks, Tracy, for the compliment and the question!
So when I set out to create Cary, I knew I had to make her different from Claire, who is the female character in my "other cancer story," Broken. I was already afraid the two stories were going to be compared, so I wanted to be sure to make them as different as possible. Claire was very outgoing, blunt, funny, low maintenance, so I wanted to make Cary the opposite - quiet, reserved, sweet, and girly.
Cary's a lot more like me in terms of her personality, and as I added in details of her life, I used things that were familiar to me - small town, same state, and her dad was inspired by my own dad. I tried to make her sort of the "every fan" too, so readers, fellow BSB fans, would be able to relate to her.
Everything else came from thinking up her back story. Once I knew that her mom died of cancer when she was little, and so she was raised by her dad and her grandparents, I could add in other details that made sense - why she became a nurse, why she has a vintage style, why she likes to take care of people and the household and so on.
So that's basically how she came together. I'm glad you like the way she's written - thank you!