Why'd this b^itch eat my pizza?

It was around half 3 am and I was starving along with my sister. So I suggested we just pop a pizza in the oven. But she was all like "no mom would be mad because it would stink up the house" and she made it clear she wouldn't help me. So I decided to make it myself (for myself) because she's such a *****.
We were planning to watch a dvd too, I was providing the dvds and suggested a Japanese horror movie but she declined and said she wanted an English movie!
I told her to set the dvd up since I provided the movie but no, lazy cow don't want to do sh'it. So I said fine i'm going upstairs then.
20 mins later the pizza was done, looked really nice! not like that burn sh'it she usually makes.
I took a small slice and put the pizza away, and went upstairs.Then 5 minutes later, when I wanted to get some more, I went down stairs only to find she had eaten about 3/4 of the pizza and then she was like "Do you want it?" (very rudely) the remaining pieces where all nibbled arounf like some rat.

Why did she eat the pizza when she said she won't help or doesn't want it? She was very rude when I asked her to put the DVD in but she decided to eat my pizza when my bro (who was also there) ate his own food!