I'm not sure if this is part of the process or not - could be. I hope for you it is part of her process and should she leave, she finds her way back to you.
It does sound like she's a little unsure of what she wants, but...
What are your options? I think you need to be prepared to tell her you love her and want to be with her and not to separate as a couple, but if that's what she needs to do to be a healthy, happy and whole person, you need to support that and let her do what she needs to do for her.
We cannot hang on to people who do not wish to be held.
I'm not saying give up on her, don't do that. Hang on to your hope, if you love her and want to stay together. Someone has to hang on and if she's letting go, you hang on to the two of you. Don't smother her, don't beg her to stay - just be steady with your words and presence and commitment to the relationship.
You are understandably afraid and confused and it's okay to voice that fear and confusion to her. Try to keep the lines of communication between the two of you open and give her the space and time she needs.
You have to be willing to ride the roller coaster if that's what it is to find out what's really going on with her.
Hang in there and be honest and strong.