What truly happened to the illusionist was that her mind was so far crushed by the glammering of Rarity that she was truly unable to think for herself anymore. The mind and soul that once were the ever so boastful Trixie Lulamoon were nothing more but shimmers which were locked away in a chest. And from that moment onward had the real Trixie died and was being replaced with a being that would be only obedient to Rarity herself and nopony else. If the blue unicorn was ever going to be released, she wouldn't be able to even function normally. Even less normal than ponies were already used from her.