We have a client who got married in 2021. They are filing MFS. She already filed her 2021 return on her own, using her previous name. We are preparing his return right now. After she filed she then went down to the social security office and changed her surname to her husband's. Which name of hers do I use on his return?

This sounds like one of those logic riddles we used to do in elementary school. Anyway, your answers are appreciated.