off her guard vs off-guard

off her guard and off-guard both are adjectives.

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

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

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

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