My current therapist is cis-F and has some considerable experience working w/ trans cis-M.
We're just now getting comfortable with her. She's new since Feb. 2015. Interestingly enough, she's "cis-F" in about the same "gender neutral" presentation as I am presenting . . . "beach casual." Lot's of denim, sweats, athletic clothing.
No sexual attraction, and I like cis-F.
What's funny is that she has ear piercings, maybe 8 or 10, cartilage piercing in the upper areas. She wears the same stuff all the time. I change earrings daily, sometimes more than once a day. And so she is always checking me out on the ear bangles. But too, she's interested that I present "male" for the most part, but wear predominately female / women's clothing. Hair past the shoulders, usually tied back.
We're at the beach. Pirates are very popular locally, and so I dress a bit like a pirate -- a bit like a biker.
But the erotic/romantic feelings one develops for one's therapist are common and entirely understandable. This is a person who listens and understands what you're feeling. Easy to develop attachments to someone like that.
Talk to her about how you feel. She's addressed this issue before, I guarantee. She will NOT be embarrassed, and she will not embarrass you.