Isabella Garcia-Shapiro is the across-the-street neighbor and good friend of Phineas and Ferb. Isabella has a crush on Phineas; however, she doesn't tell him. She's the leader of Fireside Girls Troop 46231 and often volunteers to help in Big Ideas, usually with her troop being involved.
Vote which fictional character would naturally fit in-universe with a big-named franchise! No time-travel, no interdimensional crap, no "Pooh's Adventures", they would just exist in-universe.
