I don't think she's straight?

I'm a possibly bi curious teen, and I have a friend who claims she's straight, but I don't think she is... She's my best friend since about Fall of last year. I was a transfer student, and she made me feel very welcome, and like I belonged. We soon became fast friends. She's definitely not a homophobe, I know this because we went to the gay pride convention together, and we discuss this issue a lot. Like, almost most of the time we talk. It's either that, or music. She's different than other girls. She doesn't have any interest in men what so ever. I ask her who she likes, she keeps saying no one. I really never had interest for the guys around. People have also asked her if she's a lesbian, but she ignores it. Her and I also have singing chemistry. We sing duets and post them on YouTube, and I think I'm feeling something, and claims not to be into romance, so I don't know if she realizes she's dropping signals. I don't know, it's just when we sing ballads, it just... ugh... Also I noticed one day on her YouTube favorites she had some lesbian porn video in her favorites, but the next day it was gone....I just really think I like her.. But it's not gonna work out if she's in the closet, or really ended up being straight...