I have come out to girls before, and it went well, so...
I think you should bring her someplace that's private where there's absolutely no chance that someone will disturb you, and first tell her that you like her, and that because you like her you have something that you need to tell her. Then tell her you're trans, and then if she knows anything she'll bring it up and you two can talk it over. (And chocolates never hurt anyone 😀 )
From what I've seen in your previous posts, if this is the same girl, she probably already knows or highly suspects it, so it shouldn't come as a shock to her. Just expect some questions and I think she'd be accepting of it, or else she probably wouldn't have continued to hang out with you and be touching your chest.