She means that she used $1100 on her home rental, which "ate up" half of her budget. This "ate" does not mean she used this money on eating.
Latter, she said, she only has $100/week to spend on food.
Though $400/month for 4 person is not an eye-opener in our chinese. It's not a luxury budget. The mother has to be very careful on that.
Now the article makes more sense.
Anyway, our chinese can use $1833 to live better life. I know many of our chinese familis of same size are using much less money. The major saving is on accommodation. We shared apartment or rent basement. No one will use $1100 on accommodation if they only got $1833 to use.