She is recruitable while Paul is in the party.
Nina boasts 23 Strength, that's very high, 20 Dexterity and 17 Speed, this means that Nina, like Gray, will do very well with most weapons. But her main shine is her Bare-fighting level, which is high, and with her good Strength and Speed combination makes her suitable with moves like DSC, Quadruple Kick and 1000 Hands of Kan-non. If you need an axe-user, Nina can fill this role nicely.
However, she has very low Stamina(11), her Magic power is also low(14), this means that good arnor is heavily recommended to her.
Nina is like Gray attack-wise, but like Zozma defense-wise. But you can make up with it.