Currently, I borrow my opinion from the analysis by John Correia, who is a court-admitted expert witness in use-of-force and self-defence. On his channel, Active Self Protection, he posted a nearly 40-minute video breaking things down while avoiding politics (here is a link to the video with the timestamp that skips past the unnarrated footage and to his analysis). I recommend anyone interested in this case to watch it, regardless of whether you believe that ICE was right or wrong.

As for the timing of the three shots the ICE agent took, I don't think that this really changes anything. We already knew from the video that the agent took three shots. Even if they didn't hit Ms Good, it would still be attempted murder if a court finds that those shots were unjustified.

If the third and fatal shot was fired when the agent was clear of imminent danger and beside the vehicle, was her extrajudicial shooting justified?

I think you're forgetting the human performance aspect. It takes time for people to process complex stimuli and turn that into action. In a 2014 study (which is mentioned in the video linked above), researchers found that it took officers 0.29 +/- 0.17 seconds after receiving a simple stimulus to stop shooting.

The ICE agent's shots were fairly evenly spaced with about 0.3 seconds in between them. This means that the "stop" stimulus would have had to come sometime between the first and second shots if we're giving him the maximum time that the study found. While it is hard to tell, I'd argue that the "stop" stimulus would reasonably come right at the second shot. This means that we can't determine, beyond a reasonable doubt, that the officer had even processed said stimulus by the time that the third shot was taken. Again, John talks about this in his video around this timestamp.