How to deal with people like this?

How do I respond to this? Somehow when I got home and walked towards my room, I got into an argument with my grandmother over something small. Somehow she changes the subject and bashes at me by saying that I am an ignorant failure because I chose to join the Canadian Forces. Her arrogance is superb, she says that she is a prime example of someone who is knowledgeable and that I am nothing compared to her just because she has a master’s degree from a foreign country. To this moment, I have no f---ing idea how and why she brought up this totality unrelated topic. To top that up, she said that I wasn’t raised properly, also wanted an apology from me, at this point I just ignored her and walked away. I completed my first year of university to get an advantage to improve my chances of being selected for my chosen trade (NCM), of which I received an official call 2 weeks ago from my recruiting center notifying me that I will be leaving for Basic in July. (I am still 18 years old) How do I respond to people like this who think they are all that just because they hold a post secondary education, just because you hold a degree doesn’t make you smart, I have many prime examples of individuals who hold a degree and yet are complete idiots. I made the choice to join the Canadian Forces ever since I was 13; she even knows this, she showed me her true unspickable personality and thoughts.