You realise actual humans don't think and act like this?
And do you realize that "humans" account for 7 billion people with different stories and behavior and more than once do not act neither rationally, nor consistently every single time?
So unless you want to claim that you know exactly how every single person on Earth, your point is moot. You cannot criticize a character for acting in such a way as long as it is consistent with the character.
Charlotte is borderline crazy after the trauma. So her behavior is erratic. It is convenient for the plot? Yes it is. It was also fucking convenient that MC's Emma was called exactly Emma. But that is the point of the plot: if the solution, conflict was obvious there was no story to tell.
Long story short: please criticize the story all you want. But first, get out of your high horse. You cannot claim you know how every single individual in real life behaves.
Second, criticize the story accounting for what it is trying to be. If it was a fuck fest and there was no sex, it would make sense to criticize it for it. If it was a drama with no drama, it would make sense. But to criticize a story in a fictional setting because characters with trauma act in a erratic way is almost stupid.
Fiction means not everything has to be realistic. For example, no surgeon would make her look so good after such a traumatic event in real life. Consistency is there, though: she is a person that has suffered trauma and has not deal with her issues. Never received help, never tried to heal.
And this comes from a person* that, while loving Emma pretty much more than any other player of this novel, still criticize the novel from the point of view that she is borderline a 12 years old child from a maturity point of view. But I would never claim no 18 years old girl with such a beautiful face and awesome body would ever act like a 12 years old.
*to simplify. I am actually a supervillain in the making chocolate vampire.