I would say to both trust your mistress and to remember that it takes time to develop rapport.
One frequent experience I have is to see a video and think that looks hot, and then realize IRL that its actually a lot more painful to do than I can handle!
So go slow, and dont bite off more than you can chew. And remember that you are putting yourself in a vulnerable position with someone new, and it will take time to develop rapport and comfort. Adjust your expectations accordingly.
Also, you will find most skilled dommes, like all the Fortress ladies, can anticipate and predict your responses, and that giving them more info makes this easier. So try not to 'script' your session too much in your first emails. Give them enough info to understand your perspective, but not so much that they can't deviate from your script at all based on their intuition during the session.
Tell the Fortress what you want to do, what you like, how you think about it, and so forth, and trust them to be able to adjust during the session based on your response and facial expressions.