To be sure you could get her into a big tank with a male and breed her. My jags suprised me an bred successfully at a small size: Male about 7", female only about 4" (total length) . At that rate, your female should be ready to go!
Good looking fish BTW. My male Jag says.... "hey sexy".
i would say your jag looks like a female i used to have one just like it and she grew to about 11" or so, males are more colourful and have longer dorsal and anal fins