I didn't come out to my girlfriend as trans until shortly after the new year - we had been dating for about 6-7 months at that point. One thing that was heavily on my mind before coming out is "how is she going to feel about sex now that this has come up?" In your case, your lady already knows that your identify as trans, so she's obviously okay about that. She also likely knows that you're nervous and self conscious about getting intimate and truthfully, she probably is too. I recall my girlfriend telling me that she didn't want to do anything that worsened my dysphoria and was constantly worried she was going to, but once I opened up a little more about it, sex went 0 (maybe more like 75) to 100 real quick.
I'm definitely not a vocal person in terms of sexy talk and explaining what I want during sex, but even just a little bit of guidance from you can go a long way with this kinda stuff. The main thing is being comfortable and relaxed; if your head is somewhere else, its going to be noticeable for both of you. If something feels right, tell her, if it doesn't, well tell her about that too. Communication is key!