Girlfriend refuses to cook for me but willingly cooks for a party?

[watermelon]

Sometimes i'm home really late and i jokingly ask her if she would like to cook something for me to eat. I don't really expect her to cook anything for me cause she doesn't like to cook, so i usually just cook it myself.
But the thing is, she has this party coming up and she is willingly and happily going to cook a dish for the party??? When she usually gets annoyed when i asked her to cook a dinner or something???

What do you think?