Fresh off of a disastrous meeting with her mother, Maggie spots an adorable little girl and her equally adorable dog at a gas station. They look at her, she looks at them. Maggie finally smiles. Everything's hunky-dory, right?
Not exactly. According to film critic Jim Emerson, the little girl and her pup are a sign of bad things to come:
"There's a reason Eastwood holds on the image of the little girl and her dog at the gas station…and there's a reason they're seen through the frame of one vehicle window while Maggie is seen looking at them through the frame of another. This privileged moment is a glimpse of happiness that Maggie is not going to share. It is an omen, and the inspiration for her to tell Frankie about her memories of her father and his dog." (Source)
As an allegory, the story Maggie tells Frankie about her dad having to put down his dog, Axel, is similarly foreboding. At this point in the movie, there's nothing to indicate that Maggie will have the accident she has—that's what makes it an accident—but you can rest assured that anytime any character in a movie starts telling the tale of a dog going off into the woods to die, it's not a predictor of superhappyfuntimes to come.