My T follows my lead, does not take the lead. If I were to say I need to talk about sex, she'd either wait until I explained my need further or would say something banal like, "Great! What do you need to say/talk about?"

T does not have the need/desire to talk about sex, you do So, I would make up a little speech about my difficulties with it, why I want to raise the issue, what I want to discuss specifically about it, etc. and give T something to comment/reply to? You are in control, it's your therapy.