>Her extension of stay (retirement) expires on
*****
/21 and she is returning to UK but not until
*****
/21.
If her extension of stay expires on April 8, 2021, she will not be able to get a 60 day extension of stay based on unable to travel due to COVID-19, since the last day they are selling it is March 30, 2021.
>Does she need to cancel the extension or just let it expire?
A person can change the reason for the extension of stay. I doubt the government would allow a person to change from "extension of stay due to retirement" to an "extension of stay due to unable to travel because of COVID-19"