I feel like I choose the topic nearly all the time. I think she subtly steers the conversation one way or another sometimes, but I generally don't notice it happening. She would basically never try to shift from talking about work to talking about my marriage or vice versa. Sometimes she will "check in" on something if I haven't talked about it in a while, but I am fairly comfortable giving brief answers and then saying I'm not interested in spending too much time on that topic if it isn't grabbing me.

Have you tried just telling your T that you want to talk about X instead of Y? I often find the direct approach works well. My T knows I am far more likely to "hear" her and get things out of my session if we follow what's been on my mind lately. I think I generally select my topics based on whatever is bugging me the most or whatever I'm having the strongest feelings about. If I'm not feeling particularly bothered by anything, I would be more likely to go along with something my T thinks is important.