I use to picture my T sitting beside me on a bench, like a "friend" rather than across from me when I wanted to really talk to her, tell her something specific and that helped me some.

I would use the knowledge you have that you have "accidentally" talked to her, like when you went on talking about how you met your best friend too long and got into about the mother, etc.; nothing bad happened as a result so maybe nothing bad will happen if you tell her about X? Experiment, start to tell her things that are difficult but not as difficult as the other stuff? You know you can stop/clam up well if you get scared so you are protected, use your defenses in your favor, knowing they will protect you, even when you might not want them too