I can see you girlfriend point, it's weird, but it's their life. Also, when I face some equal situations I change a few things, for example, picture them 10 years younger, she's 9 and he's 23; he's 13, she's born.

This cases is one of the ones we can think how weird it is, but it's better to keep our mouth shut and give some time...maybe they will be happy forever, or for a few months, (or weeks).