Despair's Last Journey by David Christie Murray

Paul knew that Madge and he were to have a travelling companion on the voyage, and that the companion was to be Madge's sister, but he did not meet her until he stepped aboard the steamer bound for Tilbury Docks from Adelaide. Her name was Phyllis, but for some reason or no reason her own small world had elected to call her Bill, and to that name only she gave willing answer, unless she were flattered from the memory of short frocks by being addressed as Miss Hampton. She was a child of astonishing beauty, with eyes like stars and the face of a young angel, and people who did not know her received an impression of sanctity and innocence when they beheld her. A complete knowledge of her character revealed her as an incorrigible imp, utterly without a sense of danger under any circumstances her experience had so far led her to encounter, and, apart from that, a compound -- a furious compound on either side -- of jealousy and affection.

It would, perhaps, be more just to say affection and jealousy, for Bill's heart was hot with love for those for whom she cared at all, and her jealousy was but the natural product of her affection. It was not until the boat reached Colombo that Bill condescended to accept a solitary advance from Paul. Until then she resented every minute he spent in her sister's society and every word he addressed to her, but once enlisted she became a sort of lovers' watch-dog, and held all intruders at bay.