It sounds like this is a really tough space for you to lead your daughter through, given your feelings are much the same as hers. Sending hugs to get through this, and hope the wise folk on this board can offer some suggestions of how to channel your intimate knowledge of the challenges to settle/ pre-empt some of your DD's worst fears. I found my son's existential depression terrifying; I can't even imagine what it feels like to experience it. Your description is very like his: "that life is meaningless, time is relative, and even though she's got 100 years of living to look forward to, it will pass, and once it's passed it will be as if it never happened".
And yet. There is a fundamental contradiction between that nihilist view, and what you say next:
I believe that being alive is better than being dead.
Taking as given that I have no idea what I am talking about, still I'd say: this is your key. Why? And how? It may be way harder to see that side - what makes life worth living despite it all. Can you share some of those reasons with your DD? Specific, real examples of why you feel better off alive? And (what seemed critical for us, at least), some concrete steps that would increase her sense of having some control over getting to those things/ states of being that make life worth living?
