How did she express her regret about not writing earlier?

The correct response highlights the direct acknowledgment of regret through an apology. When someone expresses regret about not writing earlier, it typically involves openly admitting their oversight and taking responsibility for it, which is precisely what an apology does. This act of apologizing conveys remorse and an understanding of the impact their absence may have had on the recipient, thus reinforcing the sincerity of their feelings and restoring the connection.

The other options do not accurately convey the action of expressing regret. Indifference suggests a lack of concern, blaming a busy schedule shifts responsibility away from the individual, and ignoring the situation completely avoids addressing any feelings of regret. Each of these alternatives fails to demonstrate a genuine acknowledgment of the missed opportunity to communicate.