My girl friend is hungry, but won't choose what to eat?

[sunn]

Alright, so here's a small problem that seems to be a recurring thing (at least once a month, and not to be too blunt and/or sexist sounding, but it doesn't always happen on her period or before etc.) with my girlfriend, and it really effects the time it does happen. Ok, so this seems to show up out of nowhere.... she'll get hungry, but won't know what to eat. So, I offer several things up, offer to go out a get her something, even scrounge in the areas of the cupboard and fridge and nothing seems to interest her AT ALL. It gets to the point where she gets pissed off because she can't eat something that she wants to eat, or even KNOW what to eat. She'll mope around about it too... I don't know what the hell to do, it doesn't seem like a big deal (and it shouldn't be), but it really bothers me... and it turns the mood of the entire day.... until she eats something. So what I'm really asking is if anyone knows what's up with this, if it happens to anyone else or what? ANYTHING will help if anyone has an idea please