Penny Halliwell

Betrayed by her best friend, who also killed her husband
Transformed from a peace-loving witch into a ferocious slayer of demons & warlocks
Responsible for writing a considerable part of the Book of Shadows
1975: Bound her granddaughters' powers & erased all their magic-related memories
1978: Became their guardian after her daughter’s death
1998: Had a heart attack & fell down the stairs, her death allowed her granddaughters' powers to return
Became a guardian spirit, provided advice & assistance when necessary