Assume for the sake of argument that she believed an intruder was in her home. Would that have justified killing an unarmed person instantly, instead of retreating outside the apartment, calling for backup, turning on the lights so she could see where she was, etc.? How far does "I was scared" get her if she wasn't even acting as a cop? And if she wins her appeal, does that get her off, or just a new trial?
You are getting ahead of me. I'll address the self defense claim next.
The appeal is asking for either an acquittal or as an alternative a conviction of criminally negligent homicide.
The argument for acquittal is question of law, not facts. It is not about any issues related to how the trial was conducted. The appellant court will make the final decision on that claim.
On the issue of criminally negligent homicide, I honestly don't know. I was going to address this later, but might as well do it here.
The charges before the jury were murder and manslaughter. Those are lesser included crimes. The appeal argues that the charges (or specifically, the jury instructions) should have been for criminally negligent homicide rather than manslaughter.
I agree with the defense that manslaughter, as written in Texas law, is not really legally possible in this case. Manslaughter would mean that she knew that she was doing something that had a significant risk of causing death but did it anyway. There is really no way that works in this case.
But the manslaughter charge was approved by a grand jury. The prosecution has no obligation (as far as I know) to include an indictment for the lesser charge of criminally negligent homicide.
This is sort of like a plea deal with the appellant court. It is saying that if the appellant court agrees that the defenses of mistake of fact and self defense holds but that the defendant did act in a criminal manner, but that there was negligence not presented at trial, the defendant will accept the lesser charge of criminally negligent homicide without retrial.