What does it mean when a girl's face "lights up"?

Anonymous
You know what I mean, you can see her whole face smile even before she has a smile on her face and after that a big smile follows. Specially if they haven't seen you in a couple of days or they don't expect you.
Updates
+1 y
I should probably rephrase it. Usually she tends to be very stubborn and acts annoyed and kinda mean(playful) when I talk to her, but if she doesn't know I'm around and I go up to her, she lights up, otherwise she acts annoyed (only to me, mind you)
What does it mean when a girl's face "lights up"?
16 Opinion