Definition of "off her guard" []

• Not prepared or vigilant (adjective)

WordNet. Princeton University. 2010.

• "Thrown off her guard by anger, Mrs Stanhope had inadvertently furnished her niece with the best possible reasons against following her advice with regard to Sir Philip Baddely, by stating that her sister and cousins, who had married with mercenary views, had made themselves miserable, and had shown their aunt neither gratitude nor respect."