Hello CommaDotSlash: Thank you for sharing this story as well as for your acceptance of your transgender girlfriend. I am an older person (around Caitlyn Jenner's age) who has struggled with being transgender my whole life.) So your story touches my heart. I'm so sorry the two of you are not meeting up for your one-year anniversary. That would have been a most wonderful opportunity for both of you.
I don't know that I have any great suggestions for you here. My thought would be simply to keep in close touch via text, e-mail, Skype (?), & even "snail-mail". Send pictures, stories, small & inexpensive but thoughtful gifts. (If the two of you each have YouTube channels, you could send each other private videos too.) Perhaps you could even send a not too expensive bouquet of flowers once or twice. Also, be on the lookout for opportunities to compliment her & let her know she is special.
I'll tell you a story. When my spouse & I were first getting to know one another, it happened to come out that she liked curly potato chips (ha-ha-ha...) So, one day, I happened on a particularly curly potato chip in a bag I was eating. I wrapped it up in some aluminum foil & tied a red ribbon around it. Neither of us has ever forgotten this. It is the little things like this that create closeness in a relationship.
One of the difficulties, in a situation like yours, is that there is always the potential for two people to unintentionally drift apart. But, this can happen to people who are physically together too. Relationships must be nurtured. And you can do so whether you're physically together or not. It simply takes additional effort.
The other thing I would say, though, is that while you can make every effort to stay close, emotionally if not physically, your gf may or may not be able to maintain this type of long-distance relationship. So you should also be prepared for the possibility that she may drift away regardless of what you do. And, of course, you are also going to be operating under the stress of your parents' disapproval which could, over time, wear on you. You'll need to be strong.
I wish you both all the best.