"Hold on. Holly J. Sinclair? As in Heather Sinclair?"
The relationship between adoptive siblings Heather Sinclair and Holly J. Sinclair began in 1994, when the eleven-month-old Holly J. was adopted by the Sinclairs. Although Heather was never seen, Holly J. mentioned her older sister several times throughout her tenure on the series.
In It's Tricky, Holly J. reveals to Manny Santos and Mia Jones in the cafeteria that Degrassi's infamous mean girl, Heather Sinclair, is her older sister. She also mentions that Heather taught her everything she knows.
In Jessie's Girl, Holly J. suggests that Anya MacPherson copy Heather's old science report project so they won't have to do the work, despite Anya's reluctance to do so. Later, when Holly J. sees Mia being nice to Anya, she gets Anya in trouble with the teacher Mr. Bince by saying that when Anya was over at her house, she copied Heather's old project.
In Live to Tell, after when Darcy Edwards falsely accuses of Mr. Simpson of sexually assaulting her to hide the fact that she was raped, rumors start spreading around and Holly J. and Anya start gossiping about it and Holly J. says that Heather saw Mr. Simpson making out with one of her friends even though its obviously not true.
In Ladies' Night, Anya encourages her boyfriend Sav and Holly J. to get to know each other. The two decide to confide secrets to one another. Holly J.'s secret is that she always feels as though she is living in Heather's shadow.
Later, Holly J.'s anxieties about her relationship with her sister are revealed to Toby. When Toby pokes fun at himself for his lack of athleticism, Holly J. tries to alleviate his feelings by telling him that she has her own insecurities about being Heather's younger sister. She says that she feels as though she has a lot to live up to at Degrassi, as her sister was popular and pretty. Toby however, cuts her off, telling Holly J. that Heather's time at Degrassi has passed, and that Holly J. is now "filling [Heather's] shoes". This makes Holly J. smile.
In Money for Nothing, the Sinclair family begins having financial troubles. As a result, Holly J.'s parents are unable to give her the money required to go to the Cheerleading Regionals in Florida. However, Heather, who is now in university, sends Holly J. a cheque for $350.00 so that she can go with the rest of the Power Squad. Heather apparently told their mother that no sister of hers would miss the Regionals.
In U Don’t Know (1), Holly J. admits that Fiona Coyne is more a sister to her than Heather ever was. While Holly J. is looking for pictures of herself as a child, she comes across old pictures of Heather, Heather's pet turtle, and their family, but none of herself.
Later, Holly J. finds out that Heather does not have a compatible blood type with her, so she is unable to donate a kidney to Holly J. Their mother later tells Holly J. that Heather had a complicated birth, which meant that she was no longer able to carry children. As a result, Holly J. was adopted by the Sinclairs.
In Queen Bees, Holly J. meets former Degrassi queen bee Paige Michalchuk at The Dot with Ellie and Marco. After Holly J. makes a snide comment about the former Degrassi students being "old." She and Paige have a face off over who is a better queen bee. Their catfight is stopped by Ellie Nash and Marco Del Rossi just before it becomes particularly heated. After Paige regains her composure, she acknowledges that Holly J. has potential, and reminds her that becoming a proper queen bee takes years of practice. Holly J. claims not to be daunted, as she has "pedigree." Paige scoffs at Holly J., and proceeds to leave with Marco and Ellie. Holly J. mentions that Paige might have heard of her older sister, Heather. Paige is shocked, and before exiting The Dot with her friends, yells that Holly J. is "the Devil's spawn."
In Ghost of Degrassi Past, it is revealed by Holly J. that her parents were visiting Heather in college.
- They were both considered to be queen bees.
- They were both on the Spirit/Power Squad.
- Holly J. mentions that Heather taught her everything on how to be a queen bee.
- In Ladies' Night, Holly J. tells Sav Bhandari that she feels like she is in Heather's shadow.
- Their mother mentioned that Heather's birth was so complicated that she can no longer carry children which then led her to adopt Holly J.
- Holly J. shares similarities with Heather's rival Paige Michalchuk.
- They both had conflicts with Paige, though Holly J.'s was in the Degrassi Mini Queen Bees.
- Holly J. is the only one to be seen on camera.
- In the 2015 interview Straight Talk with Adamo Ruggiero, Charlotte Arnold said that she would like to see Amy Schumer play Heather.