Perhaps Abuela believes that Mirabel's presence without a gift is somehow jinxing the family's magic. In the fanfiction, she might think that by imprisoning Mirabel, she can stop the negative effects she thinks Mirabel is causing. This could be related to some superstitious beliefs within the Encanto about the balance of magic and the role of each family member.
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.
Maybe she feels left out in the family. In the Encanto story, Mirabel is the odd one out not having a special gift. This could make her feel so alone and unwanted that she decides to run away.
It could be someone who is jealous of Mirabel's potential. Maybe a relative who feels that Mirabel's new - found importance in the family (even if she doesn't fully realize it yet) threatens their own status. For instance, a cousin who was once favored but now sees Mirabel as a threat.
She could run into some trouble. Since she's on her own, she might get lost in the jungle outside the Encanto. Without the protection of the family's magic, she has to fend for herself. But this could also be a chance for her to grow stronger. She might find a small village where she starts to learn new skills, like farming or making clothes. Eventually, she could return to the Encanto with a new perspective and newfound abilities.
She could go to the mountains. The high peaks are often seen as a place of solitude and mystery in many stories. There, she might find a cave where she can hide and think about her life. It could also be a place where she discovers some long - forgotten magic that has been dormant for ages.
Another possibility is that she uses this time alone to reflect on her relationship with her family. She could come up with new ways to communicate and bond with them. Since she's always felt a bit like an outcast, this isolation might give her the clarity she needs to better understand how she fits into the family dynamic.
Mirabel could use her wits. Since she has a strong will and determination, she might find a weak point in the place of imprisonment. For example, if it's a locked room, she could search for a hidden key or figure out how to pick the lock.
It could make them realize how much they've taken her for granted. They might have been so focused on their gifts and their own roles that they didn't notice Mirabel's pain.
Sakura might be initially confused. She could be thinking about what she did wrong to make Naruto stop talking to her. Since they have been friends for a long time, this sudden change would be very puzzling for her.