I'm writing a modern fantasy novel, with a female protagonist, and her principal romantic interest is another girl. I want to know how I write her without having her homosexuality being the predominant role of her character. The main plot resolves in such way that her sexuality barely affects (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 isnt used as a plot coupon to get her to the main character side). 

  So what I want to know basically is, but any other tips or examples are very welcomed:

 - When does my protagonist comes out for the reader? Should I do it offhanded, stright 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 Im not sure of how to handle it.
 - How do I avoid to people see her homosexuality over the rest of her character traits? I dont want to write lesbian romance, I wanna write modern fantasy, that just happened to have a lesbian character.