How do you talk to a transgender person? What pronouns should you use?
The general rule is that anyone who is dressed as a woman should be addressed as "she" and anyone dressed as a man should be addressed as "he".
This sounds simple, and it is. But, if someone you have always known of as "he" suddenly presents herself as "she", old habits are hard to break. And it can get complicated, such as with transgenderists who wear the clothes of one gender but still identify with their original birth sex. Or when telling a story about a crossdresser who was presenting as male at the time of the story, but is presenting as female now. Sometimes you just have to play it by ear. We've all gotten it wrong at times.
Fortunately, most of us have a sense of humor. And we understand your confusion. If you make the effort, we will forgive most mistakes.