Admiral Javas, the Judge Advocate General of Starfleet, is a Fleet Admiral according to the rank insignia on her epaulets, and according to Memory Alpha. Fleet Admiral is a five-star flag officer and the highest rank in Starfleet, and not a rank held by the JAG; so likely a prop/costume error, as happened with the last JAG seen onscreen. Previous films and series (plus the novels) have established that only two officers hold this rank: Commander, Starfleet who is in charge of Starfleet Command, oversees fleet operations and is the second-highest ranking officer in Starfleet; and the Commander-in-Chief (C-in-C) of Starfleet, the highest ranking officer in Starfleet who oversees all divisions of Starfleet (Command, Intelligence, Medical, Security etc.) and is the military advisor to the Federation President. Plus the last JAG shown in Doctor Bashir, I Presume (1997) was a two-star Rear Admiral (though the wrong rank insignia prop was used for him), just like how the JAG of the US Navy is a Rear Admiral, which much of Starfleet's hierarchy is modeled after.