How does a girl smile when she likes you?

BivTopJohnny
People say girls have a smaller smile when they like you, while friendly smiles usually show a little more teeth. What I don't get is that my crush does neither of these. Whenever I walk up and say hi to her she has this giant smile. I have plenty of close girl-friends so I know what to expect from a friendly smile but hers is a really big excited smile. The kind of smile where if you woke up on Christmas morning and saw you got a new car. Her whole face pretty much lights up and the smile doesn't go away quickly. She will keep the smile on her face even when I continue talking to her and then she will have this nervous half smile on her face the rest of the time I'm talking to her and always gives me brief answers as if she is nervous yet still has this silly smirk on her face. I just don't get this whole thing. She seems really excited and happy to see me all the time yet yet she doesn't talk a whole lot to me like she does this with her friends. Oh and bonus question: What does it mean when you look to see if her eyes sparkle/smile when she sees you? Can you physically see it?
How does a girl smile when she likes you?
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