What does the phrase "I shouldn't have told her the truth" convey?

The phrase "I shouldn't have told her the truth" implies that the speaker regrets their decision to disclose the truth. It indicates a sense of remorse or second-guessing about the act of being honest, suggesting that the speaker believes that the outcome of telling the truth was not favorable. This regret can stem from various feelings such as concern for the other person's feelings, anxiety about the consequences, or a realization that the truth did not lead to a positive situation. Thus, the understanding of this phrase aligns directly with a sentiment of regret, making it the most accurate choice.