Is Zakat payable if there is no source of income

Assalamalaikum My wife pays zakat every year on the gold jewelry she owns.This year she lost her job and there is no other (husband also unemployed) source of income to pay zakat. We have huge responsibilities of paying for the education of my two children studying in US. With much difficulty we are managing our expenses and children’s expenses. Do we still pay Zakat? If yes, how? To avoid paying zakat during retirement (as there will not be enough income to pay zakat) my wife wants to exchange her gold jewelry to Diamond jewelry. Is it permissible? If not, how do we pay zakat if there is no source of income? Grateful for your advise!