Let me begin by saying, at least you have a girlfriend..... (I've gone 24 years without anybody)
My opinion:
If you weren't travelling with her, but see her coincedentally, find a place to sit alone, and look rather sad. She'll probably see you, come to you, and ask you about what's been happening.
quote:
notice her emotions....ask her why she is happy or sad.
, Sky says. This works too, but don't ask the obvious question, "Why are you happy/sad?" or "How are you feeling?" Make a question that stays on such topic, but also some love and creativity put into it.