I don't know where you got terrorism from. The definition under question is "domestic extremism" which is not well defined. Depending on who you ask an extremist can vary between anyone who believes in the 2nd amendment to actual terrorists.
* Abortion-center bombers? Clearly terrorism.
* Oklahoma City bombing? Clearly terrorism.
* Beltway Sniper? Terrorism.
* Eco-terrorism? Such as bombing gas pipelines? Terrorism.
* Blowing up a AT&T communication hub? Not terrorism, surprisingly. https://en.wikipedia.org/wiki/2020_Nashville_bombing . Seems to be "standard" workplace grievance. (EDIT: I thought this was terrorism originally, but apparently the investigation came back and said not-terrorism)
There are some edge cases: a random shooting inside of a grocery store? Well, could be terrorism, might not be.
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Violent actions, even those that do not result in loss of life (ex: abortion bombers / eco-terrorists), that are designed to push an ideology is terrorism. Simple enough, right?
Sure, there are edge cases here and there. But in the vast majority of domestic terrorism cases, there's no controversy in the label.
The fact is the definition of "domestic extremism" needs to be extremely rigid and detailed, otherwise the government/media will use it to selectively punish their political enemies. Simply saying "you know it when you see it" is nowhere close to a sufficient definition.
Boston Marathon Bomber, Beltway Sniper, Oklahoma City Bombing. Etc. etc. Frankly, I'm not seeing too much weird selective stuff going on to be too worried about.
https://en.wikipedia.org/wiki/Domestic_terrorism_in_the_Unit...
I am guessing she had a lighter or similar - not a gallon of petrol or anything - and was lashing out in some type of way, maybe burned the back seat a square inch?
Law enforcement and the courts were happy to refer to such a (knowingly) unsuccessful burning as terrorism then. She had to deal the consequences of such.
It appears to me that some situations have higher up politicians that choose some situations will not be charged as such or 'refer to them as such' in order to signal one thing or another.