Final answer:
In 'A Dog's Purpose,' the lady in the park is revealed to be Ethan's childhood sweetheart, Hannah, leading to a reunion facilitated by the protagonist dog, Buddy.
Step-by-step explanation:
In the novel A Dog's Purpose by W. Bruce Cameron, the lady in the park turns out to be Ethan's childhood sweetheart named Hannah. The protagonist dog, who has been reincarnated several times, recognizes her scent during one of his lives as a dog named Buddy. The recognition is a pivotal moment in the story, leading to a heartwarming reunion where Buddy helps to bring Ethan and Hannah back together after many years apart.