Final answer:
The sentence provided is an example of a flashback, a literary device used to revisit past events in a narrative to add context or depth to the story or characters.
Step-by-step explanation:
The sentence “She recalled all too clearly the exact moment when her mother departed from the train station, failing to board with her for the long journey to Portland.” would be an example of a flashback. A flashback is a plot device where the narrative goes back in time to recount a past event that provides context to the current situation or helps in understanding the character's motivations.
For instance, in Ambrose Bierce's “An Occurrence at Owl Creek Bridge,” while the main character is awaiting execution, the story suddenly jumps back to detail events that led to his predicament, providing depth and insight to his character. Such flashbacks are crucial in literature as they can reveal significant formative events or hidden aspects of a character's history that shape their current actions or mindset.