You can always tell when drama is being forced because it makes otherwise pretty smart characters act like complete idiots. So let me get this straight, this random chick calls your girlfriend an "osbtacle" straight to your faces, Nagisa gets upset and tells her to stop this line of thought, then after glasses leaves and Mashiro says she doesn't want Nagisa to meet with that girl again, Nagisa asks "Why?".... What the fuck do you mean "Why?", YOU just got angry on Mashiro's behalf, don't you think the person ACTUALLY BEING BADMOUTHED would also feel angry and wouldn't want to be put trough that again? Previously Nagisa would easily pick up on that and understand Mashiro's feelings but we need to dumb her down for drama's sake.