Information needed and what should be done?

In January, 2020, my wife booked flights for us Toronto -> Amsterdam on April 22, 2020, and returning Amsterdam -> Toronto on May 27, 2020. KLM cancelled the booking for all flights at the end of March, 2020. My wife contacted her credit card company which, after considerable argument, reluctantly processed a chargeback to her credit card for all charges. Sometime after KLM cancelled all the flights it rebooked only the return flight, Amsterdam -> Toronto to May 28, 2020 which KLM did not notify either of us of, we discovered it when we logged into Flying Blue to retrieve information and we do not have the date when KLM rebooked the return flight. There is no way we can take the rebooked flight because we did not leave Toronto, we are still in Toronto. My wife does not want to contact KLM to cancel the rebooked flight because that would cause two problems: 1) A customer cancelled booking is non-refundable; 2) KLM will not provide a refund even if it cancels the flight, it will only provide a voucher. My wife does not want and will not accept any vouchers.

Information needed.
I recall that there was documentation available from KLM regarding their policy about cancelled flights that if any part of a return flight booking is cancelled by KLM then all flights are cancelled and a full refund will be provided by KLM for all flights.

What should be done?
My wife is very concerned that the chargeback for the return flight will be reversed because KLM rebooked that flight. What should she do?