The whole thing is very stupid. As far as I can tell, what's happening is:
AOC related her story in a dramatic way, where she kind of tells it as she lived it, talking about hearing pounding on the door and people screaming for her...before realizing it was a Capitol Police officer. Then she goes on to talk about being with Katie Porter and fearing for her life, etc.
Mace seems to have only heard about the most dramatic parts, the pounding on the door and the fear for her life. Not the part about realizing the disturbance was coming from a police officer. It makes it sound like AOC was saying there were insurrectionists in her hallway. So Mace says "uh no there weren't" because there weren't.
Rather than nipping this in the bud and making Mace look silly by just saying "hey, you didn't hear my whole story before commenting", AOC goes off on her on Twitter about how Mace was denying her experience and contradicting her own previous statements on how serious the insurrection was, even though saying that insurrectionists weren't in her hall specifically does not contradict Mace's statements on her own personal fear and the seriousness of the riot.
After all that's what AOC is saying too. What's funny is that they're saying the same thing, that they were both scared and hiding in their offices even though there weren't insurrectionists right outside their offices. But they're too wrapped up in their social media war to see that.
And the whole thing devolves from there.
At least that's how I read it from the incomprehensible arrangement of quoted tweets and silly drama that could have all been avoided if AOC was more direct and Mace had just gone to the primary source instead of relying on whoever falsely related AOC's story in order to score political points.