I'm writing a modern fantasy novel, with a female protagonist whose principal romantic interest is another girl. I want to know how I can write her without having her homosexuality being the predominant aspect of her character. The main plot resolves in such way that her sexuality barely affects it. (If anything, because her girlfriend is very plot relevant, and having her on the protagonist's side actually got their situation from "nearly impossible to solve" to "very hard to solve", but she would have helped anyway. The romance isn't used as a plot coupon to get her to the main character's side.)

  So here's what I want to know, but any other tips or examples are very welcome:

 - When does my protagonist comes out for the reader? Should I do it offhanded, straight at the beginning or somewhere down the road? I planned for her to give off hints over the course of the first book, and come out in the second, right after meeting her love interest, but I'm not sure of how to handle it.
 - How do I avoid people seeing her homosexuality over the rest of her character traits? I don't want to write a lesbian romance, I wanna write a modern fantasy, that just happens to have a lesbian character.