[TheConservator]

I would be interested in someone offering a moment by moment legal analysis of what’s happening.

The key moments start when he asks her what’s wrong. She responds, giving her version of the events (You pulled me over for no good reason). He doesn’t like that—even though she responded directly to his exact question.

Then, he orders her to put out her cigarette. She refuses. He then orders her out of the car. She obviously considered that order unlawful. Was it? It seemed kind of borderline to me.

[TheConservator]

During the arrest, she does say something about having epilepsy. Wonder if that might somehow be related to her death?

[BunnySlippers]

The police can LAWFULLY order you out of the car, they can search you. They can order you in the car again.

You are not allowed to say [or think], that’s stupid, I’m not going to do that.

Or you risk arrest.

[Dallas59]

The relevant Supreme Court cases here is Pennsylvania v. Mimms, the TL;DR of which is that orders given by an officer to the driver in a traffic stop must be followed to maintain the safety of the officer (like danger from oncoming cars while standing in an active roadway). A further Supreme Court case (Maryland v. Wilson) extends the officer the right to do the same thing for both the driver and their passengers. There's also this particular Texas law:
Texas law: Sec. 542.501 - A person may not willfully fail or refuse to comply with a lawful order or direction of...a police officer
So when he did order her to put out the cigarette or step out of the car, she was obligated under Texas state law as well as US federal law to obey his directions. He doesn't have to give a reason, and disobeying a lawful order can quickly become a reason for an arrest, even if it seems crazy.
Basically, if you or any motorist is ever pulled over for a traffic stop, this description quoted above is fairly accurate in any part of the country.
Basically just be respectful, don't be a smart ass, and if you're given an order from a LEO, follow it calmly and politely. If it's something you don't agree to, but it looks like it's probably going to happen anyway, let them know that you don't consent to whatever it is, but follow the order anyways.

[Moonman62]

I would be interested in someone offering a moment by moment legal analysis of what’s happening.

...

I can only guess.

There are certain questions an officer can ask at a traffic stop, such as where you are coming from, and where are you going.

That part of the stop seemed to go fine. I also believe she was right to an extent, by saying she only has to identify herself, show her registration and insurance. However, one of the things an officer can consider is whether the driver is impaired. When he asked about her about being irritated, that’s probably what he was trying to determine. If he thought she could be impaired, than I’d say ordering her out of the car was lawful.