Sorry, but doesn't it mean "why should my elder sister help you to cook rice?"
Nấu cơm is an expression in and of itself meaning "cooking, to cook" much like ăn cơm means "to eat/eating".
If that's true, it hasn't shown up in these lessons before now.
Yes ,I agree
The above answer should be accepted
What about just nấu ăn here for nấu cơm?
In my opinion is just the way Vietnamese express .
This is like in chinese or even thai they say "cook rice" . However, it should have been stated in the hint.