Haily was born in the early 2000's to an unnamed poor mother who couldn't afford her. Haily's mom placed her in a foster home.
Meeting Phineas and Ferb and Illness
During the summer, she met Phineas and Ferb while The Fireside girls were doing a charity at the foster home. A week after they met, she got seriously ill, so Phineas and Ferb put all their big ideas on hold to try to find something they could do for her. When she nearly died (the heart monitor had a glitch so everyone thought she was dead) Phineas got angry and started yelling at the rest of the group. Until he started crying on her "deathbed". Then the doctor reveals that the radiation from the microwave got it all screwy reliveing everyone. Then Phineas and Ferb discovered that the cure for her diease is to dye her hair purple which at 1st they thought was a stupid idea, then Isabella said that "either her hair dyes or she dies" so they had to die her hair purple.
After Haily was saved from death by Phineas and Ferb, she was adopted by the Verlean family, which now makes her Patricia's, Florence's, and Adam's adoptive sister.
Haily later joined her older sister's group to persue her dream of becoming a singer. And from that forward, she was the youngest and cutest member of the group.