The provided Recapy context does not say who sends those letters or exactly why they arrive now. It only notes that “letters from someone in her past force her to examine one of the most painful periods of her life,” and that this prompts Sybil to reckon with a long-unsent letter she’s been writing.
If you want a definitive answer, please either (a) upload or paste the excerpt or chapter that contains the reveal, or (b) tell me you want a spoiler summary and I’ll use any additional Recapy/curated context you provide to answer. I can also, if you prefer, offer a brief, clearly hypothetical reading of likely motives/themes (e.g., reconciliation, confession, a death or illness prompting outreach) — just say which.
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