Mrs. Zhang and Mia shares a mother and daughter love since Mia is her daughter. Their relationship was shown in several books such as Everybody's Favourite Friend: Amity, Season of Blossoms: Growing Up, My Little Secret: Privacy, Tiny Terror: Manners and More Than Friends: Feelings.
Emilia is one of the protagonists of Candy Series and one of Mia's best friends. Her relationship with Mia started when they were formed into a group together with Joni and formed the pop group Candy JEM. At first, Emilia was proud, a show off and a person who looked down at poor people like Sofia, her former friend. She also treated Mia and Joni badly at first, but then when Sofia said that she did not want to be friends with people who mingle with the poor and Joni stood up for her while saying she would not let Sofia bully her friend, Emilia was sort of touched since Joni called Emilia her friend. After that, she became more nicer and warmer to Mia and Joni and they became best friends.
Joni is one of Candy Series' protagonists along Mia and Emilia, she is also Mia's best friend. She made her debut in Reaching for the Stars: Friendship. She was friends with Mia ever since they were in kindergarten. She treats Mia nicely and was shown to be rather protective towards her, as shown when she would never let any boys who like her to try to flirt with her or being too close with her, especially Charles.
Alex and Mia shares a close friendship with each other. Alex often eats with Mia and Candy JEM during break time and is accepted into the trio during the class' group activities. Hence, the two of them bonded and acknowledged the opposite as close friends. Mia, along with Joni and Emilia were also the very few people whom did not get disgusted with Alex's poor hygiene and appearance during the events of book 4 and they even volunteered to help Alex to clean and redecorate her house.
Not much interaction was seen between Mia and Corey but the two considers the opposite as close friends and are at good terms with each other. In Season of Blossoms: Growing Up, when Mia first experienced puberty, Corey helped her by trying on her clothes as the latter suggested to help her see whether her body size is the same as Corey's. This showed the close friendship between the two.
In My Little Secret: Privacy, Corey had helped Mia and the rest by giving helpful advice to help them deal with their family problems, thus Mia showed gratitude to Corey after his advice had helped her. Mia is also the few people whom always supports Corey during times of crisis and during tournaments Corey has.
Mia and Joni also often tease Emilia's relationship with Corey in attempt to embarrass the two, this act, however, went unbeknownst to Corey.
Mia alongside Candy JEM had a rocky start with Anthony. As she found it unfair that Anthony gave Alex demerits which might cause her to get expelled even though Mia though that Alex did not break the rules. The two of them, soon however, got on friendlier terms with each other. Mia and Candy JEM are also willing to invite Anthony to join them for lunch whenever he tries to give lunch to Alex.
Along with Emilia and Joni, the trio often tease and bring up Anthony's intimate relationship with Alex.
Initially, Sofia disliked and envied Mia despite her being nice and friendly to her, often tries to bully or do things better than her to attract attention from people. Mia, however, does not seem to get bothered much by Sofia's actions of trying to overcome/surpass her at things that Mia is good at or has/about to accomplish, only on rare occasions like teasing and accusing her of "dating" Charles or complaining that Mia's photo on a page of a fashion magazine is of better quality than hers.
But as the series developed, Sofia started to loose interest in competing with Mia and soon be on friendlier terms with her. Mia started to acknowledge and got to know Sofia better, the two's bond soon got better whenever the opposite tries to help up.