The khidmah of your parents is not necessary on your wife. Hence if your wife denies to serve your parents then you cannot force her to do so. However, it is the responsibility of your wife to consider your parents as her own parents and serve them, but if she does not agree for the same then you should have some other arrangement for the service of your parents. You cannot force your wife for their service.
Allah knows Best!
Darul Uloom Deoband