Lady Olenna went down in style in the episode 'The Queen's Justice,' announcing her role in killing King Joffrey. However there was a slight difference in detail in the books for Sansa's role in the murder.
In the book "A Storm of Swords," Sansa (unknowingly) wore a hairnet carrying the poison — disguised as amethysts — not a necklace. Given Sansa's bright red hair, the hairnet may have been more difficult for the camera to see than the necklace, so that could possibly be why they changed it.