That’s all she’s really ever been. Deep down, she’s just a girl. Take away her friends, her Watcher, her Slayer powers, and what does that leave? Just a girl. Despite all the demons she’s fought, and the apocalypses she’s averted, and considering how many times she’s died, she still continues to be just a girl.
Every vampire she’s come in contact with who doesn’t know she’s a Slayer comments on the fact that she’s just a girl. And her Slayerness to them is often a shock. Buffy’s friends, the Scoobies, even mention that she needs a break sometimes because she’s not only the Slayer. She’s just a girl.
Miss Calendar, at the end of the first season makes a pointed comment about Buffy. An apocalypse is on the horizon. Weird things have been happening. To the point where Giles has to explain to Jenny that Buffy is the Slayer, and there is a prophecy that she will die.
She’s just so little.
Joyce over the years, both before and after she knows Buffy’s secret, tells Angel of Buffy’s insignificance.
So how come everyone can see that Buffy is just a girl, and everyone comments on it, and yet they all seem to ignore it and send out the bat signal every time there’s trouble. Yes, Buffy is the Chosen One and is built to fight evil. She’s here to stand against the vampires, demons and the forces of darkness, but that doesn’t mean she feels no pain or is immune to everything in life other than the Hellmouth.