This is how I see those "lapses".
What probably happened: the writer disregarded her history (out of ignorance or not remembering it well) and made her say/react in a way that doesn't make much sense given she is suppose to remember having done or lived through some stuff.
How it goes in my mind: Jean sometimes has a child-like emotional reaction to things that are happening and it feels new to her even though it's not. That's why I said it's endearing, really. I wasn't being sarcastic. I find it funny and cute.