I found that talking about the anxiety around something makes it easier to then get into the topic. Generally, t's have worked with me to find out what's causing the feelings around whatever is uncomfortable, and we find a way to make it more comfortable to talk about. When I first started with a therapist specifically for sexual assault, she knew it was there, but I couldn't talk about it. We spent a few sessions on what stopped me from being able to say things about it. I talked about the shame I held around it, and the fear of judgement. T was able to normalize some of that. It them became easier to be able to talk about the rest of it.
The other suggestions of telling t through other forms of communication, or starting with baby steps are also really good. I communicate a lot through writing or art (And much of my art utilizes song lyrics that explain my feelings). Hopefully, your t will be able to help you through the process of opening up, but you do have to clue her in to the fact that you are struggling with it...