ANSWER:

She’s not obliged to cook and clean for her parents in law. However if she does it while she’s already preparing food for her husband (which is her duty) then she will be rewarded for it. 

Kindly refer to the following link(s):

Sheikh,is it permissible for the husband to ask his wife to help with the household chores and do cooking for his parents as they are old and sick? can she disobey him in this?(she doesn’t have doesn’t have children yet) the husband can’t do cooking&cleaning for his parents as he’s at work,should she obey him?

Dealings and Attitudes with In-Laws |