Michelle Trachtenberg was a wonderful person who died much too young ... so says her "Buffy the Vampire Slayer" costar.

O’Donnell was Trachtenberg’s A-list co-star in Harriet the Spy, the 1996 kids movie that marked Trachtenberg’s first major film role (she was just 10 when filming began). O’Donnell played “Ole Golly,” a nanny and mentor to Harriet, the precocious snoop and writer played by Trachtenberg.