So? That is the law. Why do you have a problem with her enforcing the laws in D.C.? It does sound like this is a preemptive warning. Like maybe ARMED anti-ICE nutjobs are planning to show up soon. She will get them on gun charges if nothing else.
Regardless, she's advocating stepping all over people's rights because the government refuses to deal with known criminals and those who fund them.
"To ban guns because the criminals use them is to tell the law-abiding that their rights and liberties depend not on their own conduct, but on the conduct of the guilty and lawless." -Lysander Spooner
She is a Federal prosecutor. She does not work for the District. So, what Federal law are you talking about.