It Ain't a Main Dish

Ugh, I caught a cold... I sent my sister out to buy a few things, but when the door to our house opened later, the one who came in was... Yatogame? Why? What's she doing in my room? And what does "I'm gonna do what I'm gonna do" mean?! As I'm waiting anxiously to find out, Yatogame returns with a pot of miso-stewed udon and... what? Rice? I don't need rice with udon...