This book is Emily of New Moon by L.M. Montgomery. It has been adapted for younger readers by Priscilla Galloway.

"Emily Byrd Starr's mother died when Emily was just four years old, but Emily has never been lonely. She has her father, her imagination, her writing, and her cats. But when her father dies, her world is turned upside down. She is sent to live at New Moon Farm with her stern aunt Elizabeth, who lets Emily bring only one of her cats and forbids her to write in her beloved journal.

Emily is sure she'll be miserable, but she soon discovers new friends, the beauty of her surroundings, and an inner strength she never knew she had.

Maybe it won't be so bad being "Emily of New Moon" after all.