off guard vs off her guard

off guard and off her guard both are adjectives.

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

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

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

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