Sasori is the name of Dragon Eye's apprentice.
After getting inside the palace, she tries to poison Jack, Akiko, and Yamato with poisoned tea but fails due to the fact that Emi walks into the room and realises that Sasori isn't a member of the castle staff.
A fight immediately breaks out and Sasori falls onto her poisoned hairpin and dies, but not before managing to posion Akiko. Jack thinks that Akiko, who was injured in the fight, is dead, but it later turned out she was not. This fact made Jack realize that she must have somehow learnt to build up tolerance to various poisons.