I too would be depressed being stuck in a house with a little child all day long with no adult contact..
Just to give you my two cents on the problem, I think that becoming a first time mother is a drastic adjustment one has to make, whether she's PND or not. I think I was shell-shocked for the first year of motherhood. Your wife is probably missing things about pre-baby days more than Poland per se, and it would really help her if she had some structure in her week, something to look forward to and something that gets her out into the real world. Maybe a class, or a group, anything really that would ensure a few times a week she can put on some proper clothes and walk out the door without all of the accoutrements of motherhood. Probably what she hasn't put into perspective is that her reality in Poland with a child would be much different from the youthful memories of student days when one hasn't a care in the world.
Like other posters have suggested, go back together for a holiday, maybe an extended one, one that would give her a chance to let the honeymoon period wear off and see things in a clear light.
I also think knowing that one has the freedom to come and go as they please is a lot less stressful than feeling like one is trapped and unable to go where and when they want.
I hope it works out for the both of you.