Is there any way to be subtle in determining whether or not someone else is gay, straight, or bisexual?

I usually have a great "gaydar", being bisexual myself, but there is this slightly older woman who I'm extremely inquisitive as to whether she's gay, straight, or in between. This goes for many other times. With men, sometimes it's easier to tell, and in today's society, many women are more nonchalant about their sexuality. She works at my school, and she's extremely feminine. Pretty, smart and sweet, but not married or divorced, with no kids. I'm so curious. 10 points for assistance, thanks for your time, xx