Mia and Holly J. were both former Lakehurst Secondary School students and Holly J. had a dislike of Mia and would usually make rude comments about her about her being a single teen mother. In the second semester of their Sophomore year, Holly J. seemed to get catty with Mia since they both each had a crush on Sav Bhandari and matters were made worse since they had to share a locker, although Mia evicted her when having enough of her bullying. In their Junior year, they still have a slight rivalry, but seem to have it maintained on a frenemy level.
When Mia began her modeling career, Holly J. got jealous and eventually did give her share of congratulating her. When they were both Power Squad, they were teammates and eventually became friends. However, when Holly J. goes broke and becomes jealous of Mia's growing success as a model, she reveals on television about how Mia got her modeling job by performing sexual favors, and they revert back to being rivals.
Season 7 (Sophomore Year)In It's Tricky, Mia and Holly J. bicker throughout this episode. Early in this episode when Mia is talking to Manny about her crush on Sav, Holly J. jumps into the conversation and tells her that she has little luck in winning him over. They are also arguing about sharing a locker and Holly J. does not approve of the baby supplies in their locker until Sav passes by them and they swoon at him. In English class they have a debate about adoption in foreign countries and Holly J. starts to make hostile remarks to Mia. The next day at school, Mia evicts Holly J. from their locker.
In Jessie's Girl, Holly J. hates that her best friend Anya MacPherson has become friendly with Mia. Mia defends Anya, and she tries separating the two from being friends.
In Hungry Eyes, Holly J. spots Mia kissing Sav and later when Mia runs into her in the washroom she tells her while she may have been Sav's first kiss, she will not be his last, which confuses Mia. When the two see Sav and Anya together, Holly J. says that they don't need boys, but instead men.In Sweet Child O' Mine, Holly J. is the new co-captain of the Spirit Squad and declines Mia for the Spirit Squad. She gives Mia a chance to prove herself by putting her on the planning committee for the dance.
In Another Brick In The Wall, Holly J. is left out of date night with Anya and Mia.
Season 8 (Junior Year)In Uptown Girl (1), Mia sees that Holly J. is the new captain and changed Spirit Squad to Power Squad and doubts that Mia will be able to be on the squad since she has Izzy, but Mia informs her things will be different. At the school fashion show Holly J. shows jealousy when Mia is offered a modeling job. The next day at school, Mia comes with a new look that impresses Anya and Chantay but Holly J. doesn't comment about it. The next day, Holly J. warns Mia that her newfound popularity will go away soon if she doesn't get a modeling job.
In Uptown Girl (2), Holly J. eventually seems impressed with Mia getting the modeling job.In Fight the Power, when Holly J. makes a snide remark about Jane being on the football team, but Mia defends her. At the football game, Mia forces the Power Squad to cheer and applaud for her.
In Didn't We Almost Have It All, when Mia finds out that Holly J. tried losing her virginity Mia tries talking to her about it but Holly J. makes comments regarding Mia getting pregnant at 13.In Money for Nothing, when Mia becomes temporary captain of the Power Squad, Holly J. becomes jealous. The next day at school, after Leia informs her about Mia sleeping with Tom Blake, Holly J. tells a news reporter while exaggerating details and lying about Mia being a wild party girl behind the scenes and it is all aired on television as a huge scandal. As a result, Mia's once positive image with the public is ruined.
At school when Holly J. comes to practice, informing the squad she has money, they are all mad at her for trashing Mia's reputation and vote her off the squad and make Mia official captain. Despite Holly J. potentially ruining her career, Mia does not partcipate in the voting. When Holly J. reveals she is going through some things they don't know about, Mia offers advice to her about how while you can't control what life throws at you, you can control how you handle it. Despite Mia's sincere advice, Holly J. blows her off and storms out.In Heat Of The Moment, Holly J. watches the Power Squad practice and Blue staring at Mia.
In Up Where We Belong, Holly J. laughs at Mia when she announces her career for the future. When Mia decides to retry, Holly J. questions why she's even there.
- Mia: "What would I do without Holly J. Sinclair looking out for me?"
Manny: "Hold on. Holly J. Sinclair? As in Heather Sinclair?"
Holly J.: "She's my sister."
Manny: "Hold on. Boyfriend stealing, bad nose job having, puppy drowning, queen of evil is your sister?"
Holly J.: "Taught me everything she knows."
Manny: "This might be a problem. sweetie."
Mia: "I have to debate her tomorrow. Tell me everything."
Manny: "Let's just say if Holly J. and Heather share the same DNA, you're gonna have to fight fire with huge enormous flames."
Mia: "Got a light?" - It's Tricky
- They previously attended Lakehurst together.
- They were the first main characters from the Class of 2011. Although Holly J. graduated with that class in Take a Bow (2), Mia moved to France in Just Can't Get Enough.
- They were both mutual friends with Anya MacPherson, Chantay Black, Sav Bhandari, and Jane Vaughn.
- Both girls had a crush on Sav, but he was only interested in Anya, although ironically Sav did date Holly J. later on.
- Both girls have kissed Sav, but only Holly J. dated him.
- They were both love interests of Declan Coyne but only Holly J. dated him.
- Both girls were captain of the Power Squad.
- Both girls stood up for Jane in Fight the Power.
- Both had a conflict with Darcy Edwards.
- It was never mentioned or explained why they did not like each other, but Holly J. probably disliked Mia because she was a teen mom, since in season 8, Holly J. would not let Mia onto power squad because of her daughter.
- Holly J. also had a conflict with Mia's good friend Manny Santos.
- They were seen in the season 7 and season 8 opening credits together.
- Mia's late boyfriend J.T. Yorke and Holly J.'s former crush Toby Isaacs were best friends.