you tell detail in dis ()
first of all in the end there was no screaming in the end so the voices at the end could be that of the creature itself (Not the voices of Kat being eaten).
Second, and most important Kat could live because she had something else that others did not have. THE PROTECTIVE RUNES!!!, (If you are thinking that runes were for the ritual then allow me to correct you by saying they were in the "On Need" section but they were not used in the ritual so they must have another purpose, also when you take the rune it clearly says "Obtained Protective Rune")