off her guard vs off his guard

off her guard and off his guard both are adjectives.

Word	Noun	Adjective	Verb	Adverb
off her guard	No	Yes	No	No
off his guard	No	Yes	No	No

As adjectives, off her guard and off his guard are synonyms defined as:

Other synonyms of off her guard include napping, off-guard, off guard, off one's guard, off your guard.

off her guard (adjective)	off his guard (adjective)
not prepared or vigilant	not prepared or vigilant