Step to the Music — Phyllis A. Whitney

Abbie Garrett, growing up on Staten Island during the war between North and South, found herself in the midst of an explosive situation. Her mother was a Southern woman, divided in allegiance; her father hated war, though he felt the North was right.
But it was Douglas McIntyre about whom Abbie worried most. Douglas and his brother Stuart had returned from years spent in the South, and Doug had no wish to fight against Southern friends. He had been a hero to Abbie since her childhood years, and now she was afraid of what might happen. Into this already electric situation came Abbie's Southern cousin, Lorena, pretty, hot-tempered, flirtatious - and a dedicated Southerner. Lorena was ready to mix charm and recklessness in her attempt to sway Douglas toward the rebel side.
On the night of the great ball, held at the hotel on the old Shore Road, Douglas made his choice; and Abbie and Lorena were left to settle, with Stuart's help, the controversy that seethed between them.
Abbie Garrett is not a standard heroine. She indulges in no heroics, mock or other-wise. She is a natural, warm-spirited, intelligent girl. And she is deeply in love. Her family, the difficult Lorena, the Mclntyres, and all the friends and neighbors who live in this story are people in whom the reader feels a vital interest.