I think the second girl meant the first one acted weird and awkward around everybody, not just her crush, so it's not reasonable to conclude the second girl was the crush anyway.
But second girl only ever sees how first girl acts when she is around (regardless of who else is there). That's how perception works. She can't see how first girl acts when she's not there, because she wouldn't be there to see it.
That’s how I read it and dark hair was just like “wow I can’t believe I said that to someone” sometimes it takes us a while to realize we put our foot in our mouth but the interpretation that is more common in this thread probably makes more sense.