I agree with you. This is her one shot (no pun intended). I don't know what went on in their relationship or during the murder yet, but if there was DV and she was fearful or abused or whatever, this is the only shot she has to defend herself.
If you try to step back from the emotion and look objectively, she has the legal right to a defense. And if there is a 1 in a million chance that she does have a valid defense, then this is the only chance she has to present it.
I don't know if the defense has anything substantive or not. We'll find out eventually. I would hope they have something of significance to present during their case or we wouldn't be watching a trial. I can't imagine a successful self defense argument based on what, 4 days of the prosecution's case so far, but we just don't know yet.
And let's just pretend or imagine that she does have a valid defense, just for argument's sake. There is a very tight group of people with significant religious beliefs who want to protect themselves and probably their friend's image as well. People who have not been privy to the truth from TA about his "real" lifestyle. A group of people banded together to all say "he's the greatest" is pretty formidable. I don't think many, if anyone, knows the other side of him which is not an upstanding moral guy within the framework of the Mormon beliefs.