The wizarding world has had spells to help people transition for centuries. It's a natural thing for a trans individual to pursue, in order to live more comfortably and be accepted as a part of their true gender. Queenie transitioned in her teens and is entirely comfortable with having done so. However, sooner or later, Jacob finds a picture of her from her childhood, before her transition, and Queenie has to explain a few things about the wizarding world.
Bonus points for:
- Gay marriage is also a thing among wizards and has been for centuries (bonus points for side/background Graves/Newt and exploration of all the ways in which this being absolutely normal and accepted changes the way people see both trans identity and non-straight sexualities.)
- Sort of a balance with Jacob's response - he's not actively against these things and he's generally an open-minded guy, but they're not something he's used to seeing/hearing about, and he does need a while to come to terms with it.