I suggest giving her this thread via email if possible, or in person. I can understand your deeply-rooted fear, and for folks with PTSD, serious fears are magnified hugely by the disorder: I know that's an issue for me when contemplating dilemmas like this.

The trick is to let fear be your servant not your master. And I call it a trick because it seems like magic when I can do it, and heartbreaking when I can't. Right now, your fear is disproportionate.

Is she willing to play the good old game of best case scenario, worst case scenario with you, so you can play out these fearful scenarios in a more realistic fashion?

A sense of a foreshortened future or a tragic future is also just a basic symptom of PTSD, so is she able to help you with treating that? I've found that my sense of no future has eased up a tiny bit as I've done the work of processing trauma, all the stuff that led me to not have a sense of a positive, long future.

I am sorry you're struggling with this. I hope she takes your fears seriously enough to bring you to a safer-feeling place with them. You do need someone to trust with these thoughts, I'm not sure how to banish them myself without help.