First of all I would also be upset, 30 minutes late is a long time. She should have acknowledge her lateness especially if she cut your session time short.
My T sometimes starts my sessions late by 10-15 minutes but she then runs mine over so I am not short changed. Although I do not like waiting in the waiting room, I appreciate the fact that she is not rushing patients who may be struggling out the door to maintain a tight schedule. One day that struggling patient could be me.

Based on what you described in your post, I would not email her about this issue. You have no idea what the circumstances were that caused her lateness. I would try and open your next session by expressing your concern about the length of your session. You could just say something like... "you know last week we got started very late and I felt really rushed." If she doesn't offer an apology after this then I would become more direct and say something like.. "I understand in health care when dealing with people that unexpected situations arise that may alter the appointment schedule." "However, having me sit for a half hour in the waiting room and then rushing me through a session without acknowledging it was very upsetting." If she then still did not apologize AND offer some sort of compensation. I would feel free to let her know exactly what I thought of her actions. Of course after sharing my thoughts on her lack of professionalism, I would move to terminate her services. That is just me, I have an intolerance for lack of professionalism. Not providing the care you are billing a patient for is not acceptable--its fraud.