For one thing there was no robbery. That was only a theft and a misdemeanor equal to a traffic citation.
He would likely be cleared for shooting the men however because Texas law says defense can be based on a reasonable belief, even if that believe later turned out not to be true. It has to be reasonable at the time you did it. It is like a person pulling a fake gun on an officer being shot and killed. The officer doesn't have to call timeout and inspect the weapon before he can open fire. That goes to the reasonable belief. In fact the officer in Port Arthur that was clear the same day, the man that was shot and killed had a gun that had malfunctioned and could not fire.
There is no evidence whatsoever that I have seen it says she was involved in anything. She was in the passenger seat and not the driver. If you drive me to central mall tomorrow and while in there I get arrested for shoplifting, do you get arrested because you drove me there? The obvious answer should be no. Merely being with or near someone committing a crime does not mean you commit the crime. You have to take some active part.
What active part did she take in the misdemeanor beer theft that resulted in her death?