have read the whole thread, and still think you are making some major assumptions. Did I miss the bit where you said "were you triggered" and she said "yes I was"? Because anything else is an assumption, sorry.
If you honestly believe you cannot get any other therapist, and this one is better than nothing - and you want to make the situation improve instead of being able to play the victim - then say to her in explicit detail "when I said X and you responded by shifting in your chair, avoiding eye contact, and saying "'why don't we talk about Y or Z" - I interpreted your response as you being triggered by X. I'd like to talk about X. Am I correct in my assumption that you were triggered?"
But what's the point? If she has deep seated issues around sex and abhors talking about it, the best communication in the world isn't going to change that. Why would I want to keep dragging myself over there to pull teeth and beg her to talk about something she's determined not to talk about?
Also, a large percentage of body language is non-verbal. It's hard for me to write down every facial expression, every change in the tone of her voice, every uncrossing and recrossing of the legs, every clearing of the throat, roving of the eyes, mysterious silence, nervous laugh, etc., etc, etc.
And then there is simply observing her behavior.
Me: "Are you triggered by sex?"
Her: "No." Goes back to avoiding.
Me: "Are you sure you're not triggered by sex?"
Her: "I have no triggers." Goes back to avoiding.
Me: After revealing some sexual trauma. "Do you have anything to add?"
Her: Tense silence. "Not really."
Me: "I really need to talk about sex more. Can we please?"
Her: "Suuuuure." Goes back to avoiding.
Me: "I still feel like your're avoiding sex."
Her: "I'm not avoiding it, I just thought x was interesting."
Me: "But I told you I need to talk about sex, and you seem triggered and avoidant every time I mention it."
Her: "I could argue with you all day."
How long could you put up with this without going crazy?