I'm the husband of a woman who was misidentified at birth, so I'm speaking from a second-hand perspective.
For your first question: if she says she's female, she is. It's not just a matter of treating her as female, as that's just acting. It sounds as if she is female from your descriptions of her, and, thus, is not simply "acting" like a female but rather being a female - so you probably shouldn't act like she's female either, but should know she is. Now, I'm not saying you are or aren't doing that, I don't know, just that I would suspect that you could cause offense if you felt she was anything but female.
Second, as for what she likes in bed, that's something I can't even begin to guess. I would say that it is something that, like any couple, you'll both need to work together to figure out. I'm sure any possibility could exist for what she likes.
What I can speak about is this: With my wife, she appreciates my interest in learning more and speaking up as a spouse in appropriate places, as we have a close enough relationship that she knows I know who she is, and we trust each others' hearts. But when we first started dating, other than her letting me know her history, the subject just didn't come up very much, as we are a heterosexual couple doing what most other heterosexual couples do. Nor did she want me to be interested in her because of anything she went through, but rather she wanted me interested in who she is - fortunately that's pretty easy!
I'd say this - if she is like my wife, your girlfriend would want you to be attracted to her the same whether she was pre-op, post-op, or cis- (that is, identified as female at birth and today). She probably would think it was kind of creepy if someone was interested in her primarily because of what her private parts looked or look like.
That said, I recognize that there are plenty of different kinds of people, and I can only speak with even halfway certainty about how my wife would feel about a given situation. How your girlfriend feels...I can't answer that.