So she's sharing her big emotions with you, and that's fine. That's how it should work.
You create a space where she can say whatever she wants about how she feels. All of her feelings are okay. Allow her to have her cry, shout, say alarming things.That's all just her venting. Maybe she's processing feelings about past events, too.
It can be very very hard to sit with a child who is expressing emotion, I understand. But that is all you need to do in that situation. Sit, listen, reassure, but mostly just allow her to get her feelings out and release them. It sounds like she trusts you and is comfortable showing her emotions. That's good!
So those episodes where it seems to you that it's all falling apart are actually just your DD working through her emotions. I'd even go so far as to say they're not a bad thing, and may even be a positive thing! It's far worse if a child stuffs it all down and doesn't talk about her feelings. I imagine she was also anxious, maybe cried about all of those past events? But she did them, and she managed. (you could gently ask her to notice that she has felt these feelings before, that they are normal and natural feelings, common, even, and that she has handled them before and can handle them again).
You will both be fine. You may both have some emotions, and that is okay. Emotions can be hard to handle, but they are natural, and they pass.