Tina D'Amico is Courtney Moore's stepsister.
Facts and Personality
Tina is thirteen at the start of the series and in middle school, with dark brown straight hair, dark eyes, and pierced ears. Her mother, Bonnie, died when she was six years old.
Tina and Courtney met when Courtney was five and Tina was nine; Courtney felt after their parents married that she had a sister. As younger children when they first met, they got along and enjoyed playing together, riding bikes, playing with My Little Pony toys and swimming in the pool. After the birth of Rafi two years ago and once Courtney and Tina began to share a room (the one that Tina had had since she was a baby), Tina no longer got along with Courtney like before. She complains that Courtney is messy and gets irritated at anything being left on "her side." Courtney feels like there are two Tinas, "angry" Tina and "fun" Tina, and can't figure out which she might get at any time. Tina is also distant with Maureen.
Tina owns at least twenty scrunchies that she keeps organized in rainbow order on her side of the dresser, as well as extras on the counter; because of this, Courtney calls her the "Queen of Scrunchies". When she gets interested in things at the mall, she "conveniently" forgets they are on a schedule. She is interested in fashion and clothes, and Courtney has seen her use half a can of Aqua Net on just one hairdo. Courtney also thinks that she is excellent at fashion and always has the perfect hair tie for every look, and can copy any style she sees on MTV.  Maureen considers her the family's hair expert.
She has lots of friends that she is constantly talking a mile a minute with, and likes to go to the mall to hang out with them at the food court and go window shopping (leaving Courtney on her own to hang out at the arcade).
She has claimed the bottom bunk on their bunk beds for her own, leaving the top bunk to Courtney. She also owns a collection of ceramic figurines that once belonged to her mom, including a purple penguin and a carousel horse. She likes gummy bears like Courtney, to the point she never shares them with anyone.
By the end of Courtney Changes the Game Tina has admitted why she has been upset around Maureen and Tina, and she starts to reopen up to the two of them again.
In The Books
Tina interrupts Courtney right after she passes Level Nine on Pac-Man for the first time, sharply stating that they need to go. When Courtney asks for five more minutes having just beat her high score, Tina looks baffled and says "so?". After Courtney turns to start Level Ten, Tina insists again that they need to meet Mike at five-thirty at D'Amico's Electronics. She then leans in front of the screen--blocking Courtney's view--and demands to know if Courtney took her scrunchie. She blocks the whole screen saying she just got that particulal scrunchie for Christmas and to give it back, and this results in Courtney losing and getting Game Over. Tina, not sounding sad about what she has done at all, says they can go now. On the way to the electronics store, Tina stops by the Gap to window shop, then ignores Courtney to talk to a friend. When Mike introduces the girls as his daughters and Tina's friend sounds incredulous as they look different, Tina says that Courtney's her stepsister, not a real sister. Courtney is hurt and embarrased by this. When Mike shows that he's gotten The Goonies to watch for movie night, Tina says it's a nerd flick; Mike shows he got Footloose for her.
After the Space Shuttle Challenger disaster, when Maureen goes to pick Tina and Courtney up from school, Tina is sitting on the steps without any of her friends; Courtney thinks she looks younger, and her eyes are red from crying. Tina goes upstairs as soon as they get home and does not come down for dinner.
When Courtney goes up to bed, she thinks Tina is asleep (as the room is dark) until she hears her muffling her sobs. When Courtney asks what's wrong and if it's about the disaster, Tina confesses that it's not just that; anytime someone dies, she is reminded of her mother Bonnie. She speak on many of Bonnie's traits, and that she did special things with her the same way Courtney and Maureen do. When Tina sees Courtney and Maureen together it hurts because she's reminded of her mother. When her mom got sick and Tina was told there was a chance that Bonnie would die it didn't seem possible to her, even after Bonnie died, until after Maureen and Mike got married; only then did she know it was real and her mom wouldn't ever come back. She confesses that seeing Courtney and Maureen together makes her angry and sad because it reminds her all over again that her mother is gone, and it hurts so much she can't be around them. She hadn't spoken about it before because she didn't know how. With Maureen inviting her to the salon and asking her advice, and all three of them getting a "salon" treatment, she finally felt like they were a family. She apologizes for how she has been mean to Courtney, says she's glad they're sisters, and the two girls hug.
When the two are watching the news about the disaster the next day after school, Tina sniffles and Courtney hands her a tissue, knowing she's thinking of her mother.
On the day of the Dream Big presentations, Tina slips her favorite bright pink scrunchie off her wrist and gives it to Courtney for good luck.