Champlain Summer by Marjorie Vetter (1959)
Summers at Lake Champlain had always thrilled Kit. She knew all its romantic history, from its early discovery to the days when Admiral Macdonough built the fleet that defeated the British in the war of 1812. Surprisingly, her fund of anecdotes about Vergennes, Vermont, the Turners' summer address, was just the key that gave her Bates' companionship. Kit's enthusiasm for the area charmed bates and he asked her to be his guide. It was great fun touring in his cream-colored Jaguar, rowing on the lake, and picnicking near historic sites.
Kit realized that she was growing up--slowly. She began to look outside herself and try to understand others: her mother's loneliness when Mr. Turner had to be away on business trips; Great-aunt Charlotte's weaknesses; and even Elaine's good points. But it wasn't until a treacherous storm endangered Kit's life and the lives of others for whom she felt responsible that she really understood her own development into a young woman, and the ways and needs of other adults.
The historical pageant which Kit inspired proved that she had left childishness behind. "Brick Top" Kit could toss her head happily in the knowledge that her Champlain summer had brought her her first romantic interest in boys, her first compassionate interest in people outside her family circle, and her first appreciation of the heritage that had come down to her from her country and from her own ancestors. (from the inside flap)