Hi, I can relate somewhat with this, I've been seeing my therapist for a short time and I feel that every time I get overwhelmed by anxiety when going there.
What I did is that I told him that I feel I can't be open the way I wish to be because I have this fear that he would judge me or laugh at me. This helped, to make him aware of my fear, even though I still have issues opening up.

I think if you tell her about these fears, it really helps. First it brings acceptance to whatever is happening (that it is okay to not trust or feel afraid to share or just feel unable to do it for now), and that is very soothing. Then slowly you migh start to feel safer to open up, but don't rush it. (though I know how it feels to just want to put everything out there in one push...)