@Raydnt her friend Makishima-kun doesnt see her as airhead gyaru, so your conclusion is already wrong by definition.
@Renard exactly, nice choice of words - guinea pig - yes, bcs its not like she can ask Makishima "what you think about me?", knowing he'll answer "you are my friend", so she figured out that she can try to dig the truth by observing someone in the same situation, figuring out this whole "boy and girl childhood friend relationships" thing with adding to the equation another couple like them and drawing parallels.