When someone comes up with a theory they normally base it in fact, there only has to be 1 Fact in which you use to promote your theory, but there should be some form of indisputable evidence, that backs it up (
vir_cotto has taught me this well when demolishing my theories)
The fact i am looking for is a piece of dialogue or an action that promotes your theory as truth, i can currently think of none, let me dissect and breakdown your points
1. Her father being a Dick to her: there are a million reasons why this could be, disobedience, difference in morals, or maybe he's old school and expects his daughter to be a lady. there are too many things this could be to rely on this as a fact towards your theory
2:Josy calling her a Boyfriend: This one is even more trouble then #1 as now you have to take into account what we know about a whole other character. Maybe it is a boyfriend, maybe it's a girlfriend but she's embarrassed to say, the list could go on
3: Derek being supportive: This ones easy, Why does Maya have to be Trans in order for Derek to care about her?
For all i know Maya is Trans, but right now there is zero evidence to back it up.