She's a force to reckoned with specially in PVE. If she is outclassed in terms of speed/agi she will die instantly in PVP. Place her on a suitable position wherein you can kite your opponents effectively.
Flare is definitely a tank killer and dishes out massive damage with a slow casting time even Lv.20 Magic Guard + Lv. 20 Providence combo doesn't do much.
If you want her to excel in pvp specially in match battles I suggest to buff her with Casting Time -60
S tier in PVE but A tier in PVP because of the lack of innate AT reduction or speed cast from time mage. Having two AP intensive, AT mage jobs w/o speed cast is slow and bad.The fact that her ninja sub is unusable isn't a big deal because she uses it just to get the agility boost and the shadow runner passive. Even if she starts casting before enemies using her ninja AGI, her slow casting time will allow them to 🔥 or disable her before she casts. She requires magic baton or AT reducing VC and espers to compensate.