Is zakat due on my wife's gold that she lent to her sister and has not recovered for 4 years?

Your wife owes zakat (definition) on the gold she lent to her sister if her sister is well-off and not procrastinating. She should pay zakat each year on the remaining gold after the previous year's zakat, as long as it does not fall below eighty-five grams. However, if the sister is in financial difficulty or procrastinating, then your wife owes no zakat until she reclaims the gold, at which point she pays zakat for one year. It is stipulated that the gold must be intended for sale; if it is for adornment, there is no zakat on it according to the majority of scholars.