Since her childhood, the Amyrlin has shielded Elayna from the One Power for her own protection, and the odd ter’angreal is able to unlock that power. Just as the Amyrlin is about to use the ter’angreal on Elayna, the assassin and Sephraem break in, kill the Amyrlin, and take the ter’angreal as well as the Amyrlin's seal.
The Amyrlin has kept Elayna from accessing the One Power since childhood to protect herself, and a rare ter’angreal can unlock that power. Just as the Amyrlin is about to use the ter’angreal on Elayna, assassins and Sephraem interrupt, kill the Amyrlin, and take both the ter’angreal and the Amyrlin's seal.