Isabella is cheerful, fearless, quick-thinking, sweet, optimistic, caring, and easy to get along with. She is always eager to help with any of Phineas and Ferb's Big Ideas. When she participates with Phineas and Ferb in their endeavors, It's either for the fun of it, her aspiration to earn accomplishment patches, or simply to be with Phineas.
Isabella is sympathetic and would aid people who are in need of it. This was demonstrated when she showed concern for Candace, who was too nervous to call Jeremy and ask him out and when she snapped Phineas and Ferb out of their hypnotic dullness.
Being a Fireside Girls Troop Leader, Isabella is a very capable leader. She is level-headed and responsible in the face of emergencies and dislikes being told what to do by anyone, with the exception of Phineas.
As sweet as Isabella is, she can get angry. One way her temper has been flared was when someone besides her or Phineas would use her catchphrase. In such a scenario, she would express being annoyed and would often confront the violator physically.
Another was when she wasn't a subject of attention. As Isabella enjoys attention, she openly displays discontent when she isn't receiving any. She has shown this when when Phineas expressed seeing Meap as cute but not her , and when her Li'l Sparks mentee, Melissa showed Candace more attention and admiration than she did with her.
Isabella is also part of one of the Society's finest female groups for intense missions. She is also given a power-armored suit designed by Phineas and Ferb for not just her, but all of her friends for combat and defence, which she happily accepted since Phineas gave it to her .
Isabella also starring in another ultima story where she and Phineas along other random Society members were on a quest rescuing a rogue Society's secret member, Chuck Bartowski, doing a personal vendetta on the Orgs whom gave him a strange intersect download.