i'd rather be crazy than cis!
but it took me a long time to figure that out.
i think i was a girl for a few short whiles in my youth and childhood. i was also a woman for a couple years.
but now i'm more of a guy. still something less male and more girlish at times, but mostly male.
i'm non-binary though. that type of person who can't make up their mind because both answers are right. like a quadratic equation.
even when i experience losing any sense of what it was like to be a girl, it suddenly comes back when i least expect it, or in some cases, a sootball comes back after a long absence (told you i'm crazy).
i think it's a wonderful thing if you can manage to see your life as a girl as truth, rather than having lived a lie, or constantly worn a mask, pretending to be someone else. it sounds like the girl didn't have a horrible life, if that is so, then it's great for you.
so you think you're trans. maybe you really are.
but being trans doesn't mean you have to transition.
and not being a girl any longer, doesn't mean you're automatically a guy. though you're a guy if you feel like you are one.
maybe you're in denial. maybe the girl was real. both might be equally true without it making you more or less of you.
there are some thought experiments that can be done, just to figure out whether you should start thinking about transitioning fully or partially a little bit more seriously.
my favorite one would be imagining having to live the rest of your life (and you're living till you're at least 120) as either one gender, without a possibility to change it ever, and of course having to fill maybe even a little more of the gender role than you're actually comfortable with.
this thought was the most terrifying one i've ever had, and being unable to choose one made me find the somewhat different answer, non-binary.
but most people would actually choose one or the other.
if you had to choose, which one would it be?
i'd choose the guy, because i've already had enough of being a woman. done all that a woman could possibly do in her life. i wouldn't be terribly happy about having to choose, but i would choose the trans route rather than the cis.
there's nothing wrong with having been cis for your whole life up until now. people change over time, and to me it seems that unless the discomfort is extreme, it is possible to thrive rather well as one's birth sex even if that isn't really the right gender. the way i see it, a little after 20 seems to be an age when the instinct to fit in (biological function for the sake of survival) lessens so much that even people who were happy to follow the instinct, will start reconsidering their different identities. not limited to only the gender identity. when it becomes easier and less dangerous to be yourself, you might find that "yourself" isn't really the person you so naturally assumed. it takes a whole lot of discrepancy between your body, own view of yourself, and the world's view of yourself, to see at a young age that something might not be quite right. and even more to realize exactly what is so wrong.
anyway. involving yourself a little more in this community might help you find some clarity of thought, or to see other possible options. talking to an experienced gender therapist would also be recommended, it might just be that you're crazy. and crazy isn't all that bad either, so long as it doesn't cause you any serious distress.