Or it could mean she's happy, or your face reminds her of a humorously-shaped vegetable she once saw, or she's just farted and she's glad it was silent, or you're standing in front of the person she's actually trying to smile at, or . . . . . it could mean anything.
I doubt it means she wants to take all her clothes off and get 'friendly' with you.
I smile at people all the time (yes, I'm far more cheerful off-line), but there's only a very small percentage I would ever want to be 'friends' with.

"Never argue with idiots. They'll drag you down to their level, then beat you with experience."