Her Personality:

Isabelle is friendly, polite, hardworking, and eager to help the player in any tasks she can assist with. She is keen to make the town a better place to live in by encouraging the player to do tasks and Public Works Projects throughout the town.

For her, the town she works in is like a family, she knows the ins and outs of it, and has enough influence to make a villager stop undesirable behavior - such as making them change their clothes or stop them from saying an unwanted catchphrase. Otherwise, she seems to prefer to not want to confront them.

On the Valentine's day event in New Leaf, she appears embarrassed in the introductory segment and sends them a chocolate cake. This may be because of her shyness, or a crush on the player which is debatable because the letter sent to the player is about gratitude.

If the player disappears or becomes absent for a while, Isabelle takes in the workload of the mayor herself until the player returns. In Happy Home Designer, she complains about mayors destroying the town or disappearing[1], making her overwhelmed and stressed with all the work.

She's clumsy and a little bit of an airhead but very intelligent. Her twin brother, Digby, remarks that she has engineering degrees from nineteen different universities.[2]

Both siblings grew up in a cardboard box that Digby has fond memories of. The two siblings used to fight when they were puppies because Isabelle couldn't help but be mischievous and want to eat her brother's shoes. Now, they get along better, but Isabelle confesses she still feels tempted to eat her brother's shoes whenever he gets a new pair.[3]

Isabelle admitting she doesn't like confrontation

Isabelle is portrayed as gentle and dislikes confrontation.

In New Horizons, snooty villagers can comment on how easy to talk to and wise she is, and express desire in keeping her company, while smug villagers say that she is the real brains of the player's island.

Ref: https://youtu.be/myZ-IO5k9RQ