A Room in the Attic — Gabrielle Charbonnet

Molly Stewart's father always treated her like a princess, and Molly loved him more than anything in the world. But now her dad is gone, and Molly is left alone at boarding school with nasty Ms. Thacker as her guardian. Molly's friends are forbidden to talk to her, her possessions are sold, and even her pet kitten is given away. Worst of all, Molly has to live with the pain of knowing that she'll never see her father again.

But on her darkest day, when life at school seems unbearable, Molly discovers that she has a secret friend in an unexpected place. . .