Well, you did ask for the ladies' opinions. Hope I don't reflect too badly on them... ^_^
Anyway, it does seem that people are more accepting of trans-ness as something foisted upon you, whereas because they made it through adolescence without giving into the fantasies, homosexuality's a 'choice'.
Also, as noted, lesbians are immediately identifiable as such. Girl + transguy are not IDable unless they give it away. Girl + transgirl are out of luck entirely. (Oh well.)
For some reason, people tend to think that you'll be attracted to the opposite of the gender you'll hold after transition (i.e. if you become a guy, you'll like girls). For example, I like girls. My mother knows this full well. It's blatantly obvious. But upon telling her "I wanna be a girl" she says afterwards, "So do you like boys, or..?"