You couldn't work out whether it would be impolite not to accept her advances. That's right.
Du hast dich gefragt, ob es
unhöflich sei, sie abzulehnen.
I'll put up with it as part of my parental duty, but there is no excuse to be impolite to Serena.
Aber du hast keinen Grund,
unhöflich zu Serena zu sein.