“That doesn’t look to me like she was saying it’s a “possible” conclusion.”
You have made the mistake of going by the headline. Her post said “can” end life as we know it. “Can” does not mean “will”.
"As warmongers in the White House escalate tensions with Russia, let’s be real about what we’re dealing with - open conflict between two nuclear armed powers. The only place this conflict can end is the destruction of the world and life as we know it. This is what's at stake."
I just watched the video of what she said. She never uses the word “can” when talking about a US/Russia conflict. She states unequivocally that the end result will be total destruction.