It could also be due to long - hidden family tensions. Isabela might have bottled up her frustrations and unknowingly takes them out on Mirabel. For example, the pressure she has been under to always be proper and present a certain image in the family, and when Mirabel starts to question things, Isabela snaps.
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.
Since we don't have the full 'the selfish man story', it's hard to say exactly who he is. But he's surely a person in the story who is defined by his selfish actions. He could be a businessman who cheats his partners for more profit, or a neighbor who never helps others and always takes advantage of them. He is the one around whom the story's events related to selfishness revolve.
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.