How can she like you if she doesn't know you?..Friendly is a start...Go with it...Somehow figure out a way to ask her for coffee or for her number so you can then ask her out...The point is to learn more about her and figure out if you really like her.....
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If she is friendly and all smiles, I think that is a sign that she enjoys your company...If not, then she is rude and misleading...Never hurts to try!..Courage is very attractive...very!..

Courage is attractive... I'll agree with that. Maybe don't ask her out straight out, but stealthily ask her out... the ninja approach. Ask her what she's up to after class then ask if she wants to get a coffee or something. Maybe ask both girls out for coffee if they're actually attached at the hip. After all the best way to get the ins with a girl is to be cool with her best friend...