I was with my girlfriend for almost a year before she found out I was trans. I was planning on telling her, but she happened to find out before I got chance to (I was waiting until Christmas was over and she found out very late Christmas day/early Boxing day morning). I'd known I was trans for over a year before I met her, but things were complicated to begin with and I was very afraid of losing the one person who'd been able to make me truly happy. I'd been presenting as male the whole time though, but didn't bind or pack. I rarely bind now because I don't particularly need to in the colder months.
At first things were a little difficult, particularly because I had to go away for a week straight after Christmas so we didn't have time to properly talk, and there's only so much you can do via text. Once I was home again and she could see that I hadn't changed at all everything was hunky dory. It was hard for a while getting her confidence back in certain things, she was very scared to touch me because she was convinced that I would have been cringing inside every time she touched me, anywhere, but now everything's all good. She's even got used to me binding when I do (she doesn't particularly like that because of the risks), and even gets worried if I don't pack.
Talking about things is the best advice I can give, although it's not always as simple as in my case, because although we were in what other people thought of as a "lesbian" relationship, neither of us really like terming things as "lesbian" or "gay". All I've ever classified myself as is someone who likes women, and she's just open to anyone, although she's been with girls almost exclusively in the past. Talk, keep talking, and show through your actions that you're exactly the same person. You seem to have a good thing going on if she's accepting of your binder and packer, but emotional changes are a big worry for most partners.