I have never experienced anything like this and can't judge the murder victim's sister. but I can understand her wanting to vent. She is speaking on behalf of her family and probably the other families expressing their disgust at Kohberger managing to wriggle free from the death penalty and living the rest of his life at the taxpayers expense (which includes taxes paid by all the victim's families).
Kohberger can enjoy 3 meals a day, gym, library and internet and relax. the families of the victims on the other hand have to suffer loss for the rest of their lives and his murder victims of course are unable to finish their college, life with loved ones or experience getting married and growing old with their families.
So I totally understand the emotional reasons for the sisters response in court. I hope it brings some level of closure for the victims and they can get on with their lives.