Quirk of Texas law. Yes, "murder" is the unlawful killing of someone, but it ought to be the unlawful deliberate killing of someone. Killing them because you thought they were a threat ought to fall into the category of "accidental", and therefore not "deliberate", and therefore not "murder", but instead "manslaughter" or "reckless homicide."
But this is just hair splitting. The consequences would be the same as what she got, and I thought the sentence was lenient to her. 20 years would also have been reasonable. More than that, and I would think they were just being cruel for someone who did it as an accident.
Of course if what you did was justifiable (self defense, protecting your property or others property, etc,) then you are not guilty in the first place.
Yes, odd quirk. You're found guilty, you committed "murder", if you're not found guilty, you walk away with no charges. Again, seems like they should slip a "manslaughter" into the statute somewhere, but they just didn't.
You said “Killing them because you thought they were a threat ought to fall into ‘accidental’ ... therefore not ‘murder’’, but instead ‘manslaughter’ or ‘reckless homicide’”.
That actually is not how it works in many places.
Reasonably believing that a person is a threat and using deadly force against them is not manslaughter or reckless homicide. It is not a crime at all.
That is true in many places outside of Texas.