Why is my sister like this?

I know it's dumb and childish to ask or rather say, but every other day when it's her day to do her chores, she does it halfway or not at all.

I don't want to complain, but she does this everytime it's her turn to clean up and my mother doesn't bat an eye at her work, so when its my turn to clean up right after her day, I have to be the one to clean up a pot or a pan she she didn't want clean.

I just think it's unfair to me that I always have to be the one cleaning up after her day and always telling her to clean because she wants to talk to her friends all night.

Why is my sister like this?
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