Mandy

Mandy is the older sister of Thaddeus and Thor. She is driven crazy by the antics of her brothers, much like how Candace is by Phineas and Ferb's activities. She somewhat resembles Candace by the long neck and the sleeveless shirt.

During her visit to her aunt Mrs. Weaver's house, a next-door neighbor of the Fletcher-Flynns, she overheard Candace describing Phineas and Ferb's antics, and it quickly escallated into a point of pride that her brothers were more obnoxious than Candace's. She acted as lookout and cheerleader for her brothers during their fort-building competition with Phineas and Ferb. In the end, after Phineas and Ferb beat her brothers in the fort building contest, she admits that Candace's brothers are more obnoxious than her own brothers. ("Thaddeus and Thor")