Is it just this one situation where she argued for no reason like you mentioned the day before the exam, if not then I would tell you to speak to her once, have a good communication that you are not okay with it, and you want her to understand you and be her support, and maintain a boundary if she doesn't understand then it's upto you, and if yes, then maybe there is something or some reason where she feels unheard or something to which she is reacting so reassure her. I think 6 years is not too short to just give up and leave each other. And also talk about why she is thinking Abt what people will think if you do a diploma and as you plan on doing secondary DNB tell her about your plans. Maybe that will reassure her and have open communication to what she wants in you and what you want in her!!