I like both, but for different reasons.
#1 tells a mystery. It looks like she's just heard something, looked back to see what it was, and is going "Oh." She doesn't look alarmed, more like "I was hoping I wouldn't run into you."
#2 offers a bit of a resolution. She's watching something go, but she's neither excited by the departure nor dismayed. It's sort of a "yes, you're going. Now I can get on with my life" look. The expression may be "meh" like Derrel says, but for me that's part of it's charm.