This is later in the episode. She had originally pulled into the White House, said something to the Secret Service personnel who came up to the car to make her back away from the WH barricades, and then shot back and hit one of them, flipping him onto the hood of her car. Police cars (standing by, I guess) immediately got behind her but she slammed backwards again, rammed one in the side and nearly got the cop standing behind her car, and then pulled forward through the police standing in front of her, scattering them and then setting off at a high speed. She was chased for several blocks, looped around, and came to the barricade at this point (I think she probably believed that she could get into the Capitol) with the police cars pursuing her.
What you are seeing is the final part of the chase. And as for why they shot her, she may have said she was armed, or maybe that she had a bomb (they sent explosives teams to her home), or maybe it was simply because of her earlier behavior. She was delusional and she had an obsession with Obama and thought he was stalking her (well, more than he’s stalking the rest of us, I guess!). But don’t forget that they guy who shot Reagan was also just a nut with a personal obsession and did it because he thought it would make Jodie Foster love him.
I think the raised tensions created by Obama are stirring up the already crazy, which is why we have had so many episodes lately, but I think we still have to remember that crazy is crazy, and when people start acting out like that, it’s never going to end well. Personally, I think it was suicide by cop, not an uncommon thing among people having a psychotic episode.
Another thing that seemed wrong was the hail of gunfire, even though it looked like there were a lot of bystanders very close.
Yes, this clip starts with you looking down the approach to the NW steps of the Capitol, towards the traffic circle at the Capitol end of Constitution Ave. I haven't seen any footage of the WH end of this episode.
Another poster asked how al Hura just happened to be there. They were at the Capitol to film the demonstration [shutdown demonstration?]. See the knucklehead with the dollar bill taped over his mouth.