Ciel does not allow Rimuru to die, be erased, destroyed or manipulated. Even if he has to die for a good cause, Ciel won't let Rimuru die. She doesn't care if it's for a good cause as long as Rimuru is alive, she is like an omniscient intelligence that exists to keep Rimuru alive and not let him be deceived. She is immune to any mind control. Rimuru cannot die, he exists in trillions of realities and always comes back. Ciel and Rimuru are best friends, it's impossible for one to betray the other