Shelley the Shadow by Jenny Oldfield
Shelley is the smallest duckling in her family. She's always last in line and struggling to keep up - so, when her mother and siblings flee from a hungry fox, Shelley's soon left behind. Helen and Hannah save the little duckling and take her back to Home Farm. But now Shelley has latched on to the twins and follows them everywhere. Will they ever reunite her with her missing family?