DC has it’s traffic signal lights mounted on poles at curbside, not overhead. Along with fiendish traffic circles, one-ways, and all the do-nots, it’s easy for someone unfamiliar with the place to screw up.
Then, there’s the automated license plate readers. She could have been flagged in the system for almost anything.
My husband heard on MSNBC that she was doing 80 down Pennsylvania Ave. and that’s why all the cops were surrounding her BEFORE they pushed her into the WH barricades. I have not heard this anywhere else.