Call her on it! That's your job. At the moment, say, "Hey! I feel like you are implying X; are you?" That's what you have feelings for, to tell you how you are reacting to the world and help you figure out what questions you want to ask, what you want to know from the other person, etc.

Because the book is about a person diagnosed with BPD, we all have tendencies in all "mental illnesses"; they're all pretty much spectrums. Don't tell me you have never flip flopped in moods or stayed up too many hours, oblivious that you were staying up too many hours, etc. similar to what some with bipolar disorder do; tell me you have never felt down and not wanted to get out of bed, not pushed someone away for spite, not dissociated, arriving at a location/work without remembering how you got there or what you were "thinking" inbetween.

Your T liked the book enough to read it. Your T thought about you when you weren't there in front of her. Those are good things; ferreting out just what the occasion was, what the part of the book was where she thought of you and why, that's the conversation. But that's about her! SHE thought of you. That does not make it about you, for real. Next time you are reading a book, think about what you are thinking about as you read it; does that make the book "about" those thoughts of yours, your associations? No. If T was reading about a serial killer named TryinToGetBy and thought of you, would you be angry? That you get angry about the book being about someone with BPD, is about you, not the book or your T.