Some kids are gay or straight or bi or trans and they know it surprisingly early. Others take a long time to work it out (my gay nephew said he wasn't sure until he was 19). All you can to is wait and stay non-judgemental, as well as of course keeping the kids from exploring bodies inappropriately young (just the way you would do if it was her and a boy).
I've heard touching and exploring is normal, but I do think kids are sexualized too early due to the influence of what's all over the place in the media. I would not be too relaxed about a girl at 5 wanting to kiss someone romantically, boy or girl. In other words, its not the gender, she'll figure that out sooner or later, it's the age, that would cause me to have a talk with her. At 5 a kid should just be a kid.