Sarah Albert, a wealthy Spanish child, resides with her father, Mr. Albert, during the narrative’s events. She endures profound loneliness and physical illness prior to meeting Sebastian. Her isolation arises from her father's demanding responsibilities and absence of peer companionship, despite material affluence.

During Sebastian's Pyrenees journey, Sarah encounters him and forms an immediate bond. Both children share an intense desire for friendship and mutual understanding due to their similar ages and emotional voids. Sarah celebrates her ninth birthday within the timeline, closely aligning with Sebastian's age. Her health markedly improves through interactions with Sebastian, Belle, and Poochie, prompting her father's fondness for the dogs despite initial aversion.

Sarah leverages her resources and influence to provide crucial assistance to Sebastian multiple times during his travels. Her actions demonstrate steadfast loyalty and willingness to aid others in adversity. As they mature, a romantic bond develops between Sarah and Sebastian, with narrative implications suggesting their eventual marriage as adults. Belle remains a constant companion in their lives post-union. Her father's potential romantic connection to Sebastian's mother, Isabel, further intertwines the families' futures.