Alyson Hannigan acted as Lily Aldrin in How I Met Your Mother and Michelle Flaherty in the American Pie film series .
She is best known for her roles as Willow Rosenberg on the television series Buffy the Vampire Slayer ( 1997–2003 ) , Willow Rosenberg on the television series Buffy the Vampire Slayer ( 1997–2003 ) Willow Rosenberg on the television series Buffy the Vampire Slayer ( 1997–2003 ) .
Alyson Hannigan