It absolutely boggles my mind that so few people think before speaking. How on earth can you answer a question like that? I probably would have asked her something like "If I were a cross dresser, it would be pretty awkward right about now wouldn't it?" And then I would never go back to her for her services again. Rude employee = lost customer.
Of course, that is what I would likely do - what I would hope I would do is different... I would hope I would patiently, and calmly have a conversation with her about her bias and do some education. If I could just live up to the expectations "Ideal Me" has for me...
Has it ever occurred to you that perhaps for some people doing "the dreaded "P" word" IS being themselves? If not passing is who you are, and how you are comfortable - then that is exactly the right thing for you. But not everyone here is you. Some of us are not comfortable being a dude in a dress. Some of us feel most comfortable passing. For some of us, who we are is women - and being understood that way is legitimate.
Shake your head all you want, there is no excuse for this chip on your shoulder.