Retired teacher received a check for backpay from several years ago..how to handle with city form?

Retired teacher moved out of city and received a check for some money that was owed while she was still a teacher. (Several years later they finally got around to getting her money owed) Fed, State and city taxes were taken out.. all on a W2. 

She's NOW a non resident but was when employed. Also as a teacher she had the usual vacations and holidays. How do I handle this on the city form as it wants to know, for a nonresident, an address where worked and the number of days worked in the city. She was of course NOT an employee in 2018 but received the back pay check. 

THANK YOU!!!!!!!!!