Are you sure that she is cutting the sessions sure after you have a flashback? Could it be possible that you are having a distorted perception of time, instead? One way to check would be to note the time when you leave...

It sounds to me that your therapist is attempting to do things other than get you talking about flashbacks because you don't have the coping strategies in place yet to deal with them.

The more you talk about them the more intense they get and the more they occur to you outside therapy. If you are having immense difficulty with them as things are (as it sounds like you are) then it would be counter-productive to get you spending more time on talking about them.

1) Build coping strategies
2) Process trauma

If 1 doesn't happen before 2 then the client can be overwhelmed (it sounds like you are a bit already).

Can you talk to her about your concerns?