Interesting point of view, Nafany.

If the clue is correct, then there are many options in which ways SG could develope this hint:
1) In Freddie's mind, the trigger word of Evie works as predominant than the (previous) trigger word of Carmilla.
2) The trigger word of Carmilla will remain still stronger than the one of Evie, and will erase all her attempts to subdue Freddie.
3) Both trigger words will neutralize each other, and Freddie will break free from every external control upon him.
4) Both trigger words will MIX each other, with impredictable results to both Evie and Carmilla (the only sure thing is that Freddie will freak out!)
Of course these are just hypothesis. Maybe SG means to bring the plot in a total different direction; after all, we have not idea about the original plans of Carmilla towards her nephew (btw, as far we know, he is the ONLY male in the LeFey family; Carmilla could have planned a special role for him, in the coven).
That's the main point (not to say the
only point) to consider thinking about the further developments of the plot.
Indeed, SG do not make all his efforts just to be praised by those 5 billion readers which give him not a cent; he must (and I say
MUST) listen and make happy his few subscribers, which guarantee him a
concrete reward for his precious time and his hard work.
So, if the majority of his subscribers ask for the blood of Trixie or Country Girl or whatever else evil thing they want to happen...
then SG has to follow their wish, despite the disappointment of all other common lurkers. That is. Nothing more, nothing less.