They are masked men in an unmarked car. They could easy have been someone seeking to harm her. Additionally I've seen reports that some of the approaching agents told her to move to get out of the way while others were demanding her our.

Regardless these are immigration agents. They had no authority over her in the first place. The car ahead of the group that shot her was able to pass with no problems so she wasn't obstructing their path and reports show she was encouraging them to go past.