You say you think about what you will talk about before your session. Is there any possibility for you to hand her something (just bullet points or main 'themes') written so that *she* can help get you started and/or probe or gently 'push'.

Or if she does email you could send her the main points. Can you ask if she allows that?

At any rate, be frank with her and let her know how hard it is for you to open up & that you would appreciate her help in getting you started and if she has tips etc. At least she will understand where you are coming from & that it is not stubbornness or not wanting to do the work that is stopping you. More importantly, she might help draw you out. Can you ask her?