I think the agent positioning himself in front of the vehicle like that was tactically foolish.
At the time he first pointed his pistol I did not see a lethal threat.
This is a tough situation. She does appear to strike the agent. However I would say that by the time the weapon was fired she was no longer an active threat and she was fleeing.
It did not look to me like she was attempting to hit the agent. It looks to me like she was terrified and fleeing. It looks to me like he fired out of anger not self-defense. But I wasn't there and I wasn't in his mind so I can't say.
What was the reason for them trying to detain her in the first place? Did they have Reasonable Articulable Suspicion that she was guilty of a federal crime? Did they have a warrant for her arrest?
If this was an unlawful detention then the agents lose the right to claim self-defense. If this was an unlawful detention then I would say she would have the right to use force to avoid the detention. Exercising that right however could be a tactical mistake.
Edit: remove statement that in hindsight was unnecessary.
Edit: I have to look more into this and find more information. But those are my initial thoughts after viewing the first video. After finding more information my opinion may change.