We had received our grades in class and compared them. Can you interpret my ex-girlfriend's reaction?

After history class my ex-girlfriend, sitting in front of me, showed me her semester grade. I was not happy with my own grade. She asked what my grade was, and I told her, with shame. It was one grade lower than hers. She then smiled/smirked, and then turned back around. Why did she have that reaction?

Thanks.

We had received our grades in class and compared them. Can you interpret my ex-girlfriend's reaction?
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