Sometime before the special, Isabella managed to get the spaceship from an unknown source. She then used it for the Kessel Run, where she was supposed to beat it in under 11 parsecs until Han Solo intervened.
Later, Isabella used the spaceship to bring Phineas and Ferb to the rebellion in order to give them the Death Star plans. Sometime after they arrived at their destination, Isabella left with the spaceship as Phineas went to look for his brother.
The spaceship is silver in color with pink/purple propulsors at the sides. It also has a pink window. As its name implies, it bears a resemblance to the head of a Chihuahua.