There are quite a few out there. Some fanfictions might focus on the emotional aspect of Mirabel being adopted. Like how she initially feels like an outsider in her new family but then gradually finds her place. Others could be more about the plot - driven adventures that her adoption sets in motion. For instance, her adopted family might be part of a secret society and her presence there uncovers all sorts of secrets and mysteries that they have to face together.
You can start by searching on fanfiction platforms like Archive of Our Own or FanFiction.net. Just type in 'Mirabel adopted' in the search bar and see what comes up.
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.
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.
She might lose the trust of her family members. In the Encanto family, trust is crucial. If Mirabel lies and is found out, her family may start to question her honesty in the future.
One possible reason could be that Mirabel might have accidentally broken an important family heirloom. In the context of the Encanto family, their heirlooms are often tied to their magic and family identity. If she damaged something like that, Abuela, who is very protective of the family's traditions and magic, would likely punish her.
It could be Abuela Alma. Since Mirabel getting a gift would have a huge impact on the family, Abuela's reaction and her journey of accepting this new change in Mirabel could be a major part of the story.