I really like this girl and she goes to my school's GSA (gay straight alliance) but she hasn't outright said she's gay!! And my sister said that she heard her say that she's straight. Is it possible that she's just closeted?? she's gone to almost every GSA meeting. :/
Maybe she's straight and trying to be politically correct or supportive or something. The only way to know is to talk to her, silly. Just start talking to her, then eventually ask if she's seeing anyone, and maybe who she's into? Or maybe ask if she has a crush on anyone.
It's also possible that she is straight and is there to support the LGBT community. It's not unusual at all. But you'll never know unless you ask straight up.