It could also be unintentional on his part. My husband often dismisses my concerns over certain things because he will think I am hearing or seeing things. I have to show him for himself sometimes. Which is a form of gas lighting, but at least he apologizes and admits it when I’m right.
Tell her to look up the definition of “Normal” in psychology. She’ll find there isn’t one. Psychology is nothing but problems, and they are easy to find in almost everyone if you want to (to different degrees of severity), but you can’t go around accusing everyone of being nuts. People just learning psychology don’t realize this, they read a bunch of problems and see them in a lot of people, some psychology students start seeing problems in themselves and get paranoid. At some point you have to take psychology with a grain of salt.