Hi hannahh. If Susan's okay with it then obvs so am I. Nice to know people are interested in trans stuff! I'll just post what I've got to say here, rather than PM.
My birth name is Joe. I was never particularly happy with it, before I realised I was trans. When I came to that (sudden) realisation at the age of 22, I wanted to get as far away from my male identity as possible, so I tried out (online etc.) uber-female names such as Cecelia, Leila, Victoria, and so on. As I tried out living as a woman - social transition etc. - I started to accept certain things about my masculine life. I came to see myself as a sort of tomboy. I decided to keep the letter J, because it's cool. Then, I wanted an English name that was long-ish, but could shorten to something still unambiguously feminine. Jennifer was basically the only option, so I've been using "Jenny". I've been trying it out in real life, and I'm mega comfortable with it - partly because I'm 6'2 and think anything super-glamorous would sound a bit silly - and so, at this point, I think Jenny will stay.