I make sure to pick the same gender therapist as I am. I would not want to talk about sexual things with a man. I have been in therapy now for about a dozen years, starting when I was first diagnosed with PTSD. It has gotten easier over the years, but I must admit that talking about sexual things, especially the child molestation was hard at first. I wrote about it here in my trauma diary and then found it easier to talk about after that. That was about 2 years ago. I don't even feel the need to talk about it now, since I unburdened it in my trauma diary here. I talk about things that are happening in my life now and also anything from my past that seems to relate to what I discuss. My therapist also tells me of experiences from her life that seem to relate to the things that I talk about and tells me as well how she deals with those things in her life (or solves them). I really appreciate that part of it all, as it is good to get her viewpoint upon things from her own experience. Somehow, when I look at things from her perspective, it makes it easier to view my own life and then deal with it. She told me once that she uses a mixture of various therapy techniques to do therapy on me, not just one. I guess, according to whatever comes up, that gives her a wider assortment of tools to help me with and that I love.
As to how to do it, how to talk freely, you have said that you now trust her, so that is the first step. I had a therapist once that crossed her arms over her chest during therapy. I did not like this, as in the field of body language, it is a very bad sign. It is like she was protecting herself from me or my ideas, so I quit her after a few months. I first pointed it out to her and said I did not appreciate it. When she did not change after that, that was when I quit. So you do need to feel comfortable with your therapist.
Next, you need to discuss with your therapist how you feel about talking with them. It may be that you should ask point blank for help with this. Ask how it could be made easier to speak about very personal things. My therapist has stuffed animals in her office! You would not believe how much I like this and how much easier at makes it for me to open up to her. Somehow, this makes up for all the stuffed animals I never got as a kid and all the pets that I was denied too. Do ask how you should talk about your life, How to speak about very personal things, ask for pointers on how this could be made easier by the therapist too.