Question about act 4 cassia story AGAIN [big spoilers]

Is there just no way to get cassia taken over by her evil grandmother? Ive tried every single option on her book scenario. Ive failed and chosen every single physical combination with no luck. The alternate timeline RT in the final area mentions she got corrupted so was that just a hint of what they COULD have done? Idc if you spoil how to do it just tell me if you can or cant. And if you cant WHATS THE POINT OF EVEN MAKING ME DO CHECKS IF I CANT FAIL?