This is a case where the justice system is irrelevant.
I’ve known twins including twins who had one die.
Despite any animosity, the death of a twin is a maiming of the surviving twin. They usually don’t last long. In my experience, never more than a year.
I know twins tend to be close, and often so close they’re enmeshed. These two most definitely were. One story says that while they dated, they “knew” they would never marry. And they had a very tempestuous, even violent relationship. The Palm Beach Post story also speaks of how their older sister was violent towards their father.
I disagree, though, that the justice system isn’t relevant. It really can’t base its decisions on the closeness of twins. They weren’t two persons, and they were adults and understood that.
And this twin not only endangered (and ended) her sister’s life, but endangered the lives of other people as she drove recklessly.