At her wish, their first meeting had been clandestine.

Why?
Both their families knew of their mutual affection.

Therefore, why should she now make a secret of their meeting after twelve months' separation?
He was puzzled at her note, and he was further puzzled at her attitude towards him.

She was cold and unresponsive.

When he held her in his arms and kissed her soft lips, she only once returned his passionate caress, and then as though it were a duty forced upon her.
She had, however, promised to come to the ball.