Well, of course, there's the new girl herself. She's usually an outsider, maybe having moved from a different town or even a different country. Then there's the mean girl or group of mean girls who see the new girl as a threat and try to make her life difficult.
Often, there's a romantic plotline where the new girl catches the eye of the most popular boy in school. Maybe they start off on the wrong foot, like in a classroom argument, but then as they get to know each other better, they fall in love.
Participating in group projects is also a great way. If she gets involved in class projects, she'll have to work with other students. This gives her a chance to show her personality and skills, and also get to know her classmates better. For example, if she's good at art and is in a group project for a presentation, she can contribute by making nice visual aids, which will make her more likable to her group members.
There could be a friendly teacher. This teacher notices the new girl's struggle to adjust and offers her support and advice. For example, the teacher might give her tips on how to make friends or deal with schoolwork.
At a new school, a girl named Sophia was in an art class. The teacher asked the students to pass around some paintbrushes. When the brushes reached her, the boy sitting next to her tickled her side a bit while handing them over. Sophia squealed in surprise and laughter. This incident broke the ice between them, and they often shared a laugh about it later, making her new school experience more enjoyable.
There was a new girl in school, Sophia. In the art class, the students were having a relaxed time. Sophia's同桌 (deskmate) accidentally brushed against her neck in a ticklish way. Sophia let out a little laugh. Her同桌 noticed and then started to gently tickle her neck as a joke. Sophia tried to dodge but was smiling all the time. This little incident added a touch of fun to their boring art class.
Perhaps she is a time - traveler from the future. She has knowledge of future events that will endanger the ninja world and Sasuke. So, she tries to enlist his help, and in the process, a relationship develops between them. She might have unique abilities due to her time - traveling origin.
Perhaps it's a long - lost relative of one of the existing Order members. For example, a niece of Sirius Black who has just come into her magical powers and is eager to help the cause. She would bring a new dynamic with her connection to an established character.