In The Vampire Diaries Season 4, Episode 21, “She’s Come Undone,” the witch made a deal with the doppelganger for Silas’s tombstone. “You’ll get the one thing you want most in this world,” she told Katherine. “Freedom. Survival. Never having to run from anyone ever again.”
Bonnie promises that after the veil is dropped, she’ll persuade Qetsiyah to perform the same immortality, invulnerability spell that she did on Silas. Naturally, Katherine agrees to the swap.
This idea — making Katherine an even more powerful, unkillable being — is the exact opposite of what Elena (Nina Dobrev) has in mind. She blames Katherine for ruining their lives and has decided to kill her doppelganger. How could two supernaturals — who can both blame Kat for Jeremy’s (Steven R. McQueen) death — reach such different conclusions?
This is why we think Bon-Bon might be playing Katherine. OK, the witch hasn’t exactly been sharing her extracurricular activities with the rest of the gang (no one knows she’s planning on dropping the veil, right?), but we can’t really see her really making Katherine uber powerful.