Those ladies
So here's a couple things I've noticed about some terminology. I'm not a stickler for this sort of thing, but something about your wording made me want to share.
A transvestite, while technically referring to either gender wearing clothes of the other, in practice typically refers to a man wearing women's clothing. This does not mean that this person is gay or transexual. According to Eddie Izzard probably the most famous transvestite, it's basically being a "male tomboy". Without further information, there's no reason to assume someone is gay or transexual when hearing the term transvestite, and thus no reason to refer to transvestites as 'ladies'. Depending on the transvestite, it could even get you into a fight.
A drag queen on the other hand is a gay man dressing as a woman. I haven't seen an instance where a drag queen genuinely cared whether you referred to them as male or female. Most drag queens I'm aware of are pretty ballsy and gave up giving a fuck about what people say a long time ago. See Willam.
A transexual is a different story. Being a transexual seems to be a very difficult ordeal that can be very hard on people. Transexuals are much more aware of the pronouns used to refer to them. If someone is male-to-female, they want to be called she, and if they're female-to-male, they want to be called he. Regardless of what stage of the process they're in, using the right pronoun can really make a transexual's day. When a transexual is trying to pass as their preferred gender, the term transvestite doesn't really apply. I don't really know of any examples for this off the top of my head, but one probably isn't too hard to find.
Not trying to sound SJW-ish, I just like words.
TL;DR: Transvestite =/= Drag Queen =/= Transexual. And I wouldn't call transvestites "ladies".