When a flashback happens part of not being able to talk is that our brains store memories in different areas, some of these area do not have language.

If you therapist knows about PTSD she should know what flashbacks are. Maybe you can google it and see if there is a discription that helps you put it into words. YES, when having a flashback the brain/mind is re-experiencing the event as if an individual is experiencing it in the now. Emotional flashbacks are like that too, I experience these myself.