Hollyhock, a Spirit of Mischief by L.T. Meade

The whole circumstances of the case kept Jasmine wide awake during the greater part of the night. She slept and woke again, and each time she slept she saw a picture of her naughty sister Hollyhock and of that unpleasant girl, Leucha Villiers, clinging together as though they were, and always would be, the very greatest of friends.

Now Leucha, in her way, was quite as troublesome an inmate of the school as was Hollyhock; but whereas Hollyhock was the life and darling of the school, Leucha, the uninteresting, the lonely, the proud, the defiant, the cold, cold English girl, chose to be alone with the single exception of a friend, who was as uninteresting as herself.