No - unfortunately your wife cannot sponsor her sister for PR.
If you want your sister in law to come to Canada to work as a nanny for you, she would have to apply for a work permit through the live in caregiver program. As a first step, you would need to obtain an approved LMIA. You would also need to ensure you have enough income to pay a live in caregiver salary - and also enough room in your house/apartment to accommodate another person.
For your sister in law's work permit to be approved, she will need to have at least one year of full time paid work experience as a live in caregiver within the last three years - or six months of full time related studies in the past three years.