I think her greatest weakness is that she is so squishy, especially if you're planning to use self sacrifice. her AI might also tend to try get closer to enemy since she don't have bow subjob so she can't attack around allies or other obstacle.
so maybe if you're aiming to get her, you might need to have kitone or vinera's TMR that can lower hate. or use anything to increase her attack range.
She has the similar problem to Lu'Cia, who I use in everything on Global. Odds are, if they use a tank with Hate Up, (esp WoL) at the current meta, mages will still chew her up. Worse still, Luartha lacks Reflex that both Frederika and Lucia get from Ranger subjob, so she won't have that buffer to save her. So she's good, but she'll still have plenty of problems in PvP with tank aggro
I love her design and her ranged damage potential is so great, but hot damn what a bad TMR she got. I mean even a +5 capella is much more viable option than her own gun. it's so wacky
similar dmg to an ras algethi critical, and also has % to stun, is a pretty good weapon for her, not for others gunners who nee a dmg boost, because she already have all the dmg needed with self sacrifice+tune up.
Gunner with Def Piercing and self secrifice
( Lot of Damage )