There's your problem. My GF was grumpy/sad when she didn't know anyone in London. I was at work all day, and she was just studying by herself all day. Little issues suddenly become very big issues.
Just think of this: when you come home from work, you'll probably be the first person she sees that day.
Something as innocent as buying a tie or being on SF for 15mins can suddenly become a big issue, even if you spend just as much money or more for her. It's not really about the money, it's about the attention. Even doubly so because she moved to a different country, being entirely dependent on you, because she doesn't know anyone else. I can imagine that must be quite scary for her.
Having friends solves this issue.
EDIT: What SB said.