I think its important to see the difference between “it wouldn’t matter at all if I died” and “the world existed before me and will continue to exist after me and I’m a very tiny detail in the grand scheme of things.”

I think she did you a disservice by turning your statement around and applying it to herself. I think she was awkwardly trying to tell you that no one, no matter their position, is irreplaceable at work. But really, the question is: what is your existential anxiety about? Is there some part of your Work (not your job) that you feel like you’re not getting to?