We were talking about what is going on at the psychologist.
Was it casual? surprised or ?
It's not impossible for it to be another mental health issue that just happened to present itself along with BPD. Also, its interesting that you said
"parts of her that feel totally her at the moment.", and not different entirely.
Anyway, we all have "personas", images of ourselves we have. like I might not behave exactly the same at work, at church, or at a family gathering, but I understand that they are all "totally me", and can for example let go of my "professional self" at a party, hope that makes sense?
Anyway, details on this one would be very important to help you figure out if it is a "compartmentalization" sort of like I mentioned last paragraph or something else entirely.