She was an exchange student at school on the first trip out, no? It's possible she opened up over time being out-of-country, the game never really shows that. She attributes a lot of her problems to the control of her father. If you believe her story, that's probably why. He seems very traditional and strict.While I don't know what the hell y'all are talking about exactly (as I said, I just started playing), I would like to chime in.
If she is shy, or reserved, and quiet now. You have to take into consideration she's been living in Korea for over a year. Women there are more reserved and quiet there. From all I've seen of their country. They don't go wild like American women do. So I can understand that being her personality now.
If like others here, you think she's just lying about it all, then I'm not sure of why the change. And there'd be no reason for her to return as she got away from the MC... so why come back at all? She's certainly not gloating to the MC about it.