As you have gathered I am vehemently opposed to any kind of trigger warning on books as it will inevitably morph into something else. Either censorship, indirect control of authors/editors or outright condemnation of existing works.
I do sympathise with your friend although am surprised. My experience with PTSD and Complex PTSD is largely trauma based where it has been medically diagnosed and at least partially understood. Those suffering tend to avoid triggers which tend to be sensory and instantaneous, locations or situations. Movies and TV are likely to get there before you are aware or you don’t watch in the expectation of having problems.
Reading strikes me as more abstract but if it can still triggers you friend then doing exactly as she is doing seems like the solution. To create a list of every potential trigger and apply them to every book is not only a monumental task but one which will continuously grow as more potential triggers are added. Where do you stop?
I also feel those who felt it necessary to let Joe know why they stopped reading his book may have been indignant and outraged but not traumatized. I am also sure that some of them would disagree and explain at length how they mourned a fictional character for months. Perhaps that is testiment to how well it was written?
You have the choice of how to rate a book and one can only hope it is honest and based on the quality of the writing. Personally I wouldn’t down rate a book for offing a character that it has built up and if I stop reading it is because I have had enough of either the story, laziness of the author or because suspension of disbelief has not been achieved or been broken.
I despise those who will rate at one star on Amazon because they feel the book is overpriced. It tells you nothing about the story and skews the overall rating. Rating down because Brand died and it broke the big romance with Thorn
opened a whole new path crucial for the ending. It is just petulance on the part of the reviewer and about Punishing the author, not about how good the book is. I hate to think what the GOT one star reviews read as. one Star you killed...
I tend to avoid what I don’t wish to read and use my judgement as the final decider. While I will listen to others opinions the final decision on whether read a book is mine alone. That should be true of any adult and for them to seek advice from those who have previously read the book or read reviews is their responsibility. Those with reason to be cautious should do so. Apply common sense and books are really easy to find out if they are suitable as it is.