I know the $250 credit is renewed every cardmember year, but in this case, what exactly is the cardmember year?

My wife applied for Surpass a few years ago on 5/31. After a year, she downgraded to free Hilton card. On 12/2/18, she upgraded to Aspire and was charged 5 months of the annual fee January 2019. So does the $250 renew on 5/31? 12/2? Or the date in January she was charged the annual fee? She used her credit late April to early May.