I'm going to confront my sister about things she said while grieving
What do you want to confront you sister about?
It's because she's an awful person who wants to kill others
You shouldn't excuse your sister's behavior, but you should have compassion for her if she's grieving. Sometimes people say things they don't mean when they're upset. Confronting her too harshly might worsen her grief.
You're right. I'm not going to say anything to her right now.
That is a good idea and try to be supportive of how she is feeling. She may just be feeling moody or in a bad mood generally. That being said, it may be a good idea to talk to her about the words that are coming out of her mouth and what they can mean to others.