Perhaps she tries to understand Abuela's perspective. Mirabel is a kind - hearted girl, and she may think that there is a reason behind Abuela's actions. So she might try to see things from Abuela's point of view while still feeling the pain of the punishment.
Mirabel might be initially shocked and heartbroken. She loves her family and the village, so being banished would be a huge blow. She could cry and try to plead with Abuela to change her mind.
She might be heartbroken at first. After all, being kicked out by her own abuela is a big blow. But then she could become determined to prove herself. So she might set out to find a way to show that she is an important part of the family even without a magical gift.
The younger characters in Encanto like Antonio would be excited. He loves stories and new ideas, so Mirabel fanfiction would be like a new adventure for him. He might want to share it with his animal friends. And Dolores, with her ability to hear everything, might already know about the fanfiction. She could be either intrigued or a bit worried depending on how the fanfiction is being received by the rest of the village. If it's causing a stir, she might be concerned about the family's reputation, but if it's positive, she would likely be quietly supportive.
At first, Mirabel might be shocked and confused. She would probably wonder why Abuela would do such a thing to her. She could spend her initial time in prison trying to figure out what she did wrong or if there was some mistake.
There are also some Encanto - specific fanfiction communities on social media platforms. For example, on Tumblr, there are often users who share and recommend Encanto fanfictions. You can search for tags like #EncantoFanfiction and #Madrigals to find some great reads. Additionally, some Discord servers dedicated to Encanto might have channels where fans discuss and share their favorite fanfictions about the Madrigals.
One interesting storyline could be exploring the unshown daily lives of the Madrigals before the events of Encanto. For example, how Julieta manages to cook such magical food every day and what kind of experiments she might have done in the kitchen. Another could be a story about Bruno's time in the walls from the point of view of the other Madrigals, like how they might have unknowingly interacted with him without realizing it was him. There could also be a fanfiction focusing on the younger Madrigals and their playtime, and how their powers influenced their games.
It could be her mother. Mothers are often the ones who enforce discipline in the family. Her mother might feel disappointed in Mirabel for lying and give her a punishment to teach her a lesson.