This is the first time I’ve heard that. I poked around and found this article to be the most informative:
https://www.redstate.com/jenvanlaar/2019/04/02/aoc-really-economics-degree-boston-university/
Looks like she double-majored at Boston University, in International Relations and Economics.
Do you have a more definitive source?
If she has 12 credits in economics she has a minor in economics (at best), not a double major.
She has a B.A. in International Relations. Period.