| This Catria is meant to be a flier team off-tank, also able to do damage. She is best on a flier emblem, but no emblem is ok too.
As for her ivs, attack is the only stat she can get away with lowering, as speed prevents her from being doubled, resistance keeps her especially alive against magic users, while defense focuses on non-magic units, and her hit points generally are working to keep her alive against all forms of damage. The stats she can not lower, she heightens with a boon to increase her survivability.
As for the weapon, Berkut's Lance+ basically give her a resistance boon on enemy phase, allowing her actual boon to be in another stat. For this weapon an hp boon is recommended. Firesweep Lance+ allows her to not get any counter attacks (or counter attack enemies either). A defense boon is recommended for this one. Those two weapons were for a strictly defensive set. If the player wants a little less defensive, but still very good defense and resistance wise, but wants a more offensive presence in their tank, then Brave Lance+ is the best weapon. With Brave Lance+, a speed boon, and Fury 3, she can reach 35 speed, so a speed boon is preferred to increase her chance of not being doubled (or quadded) and her chance of quadding. For equally defensive versus offensive weapons, the Slaying Lance+ is as best as it gets, though her budget Killer Lance+ is ok too. With those general weapons, a general hp boon is the most preferred.
For all fliers, reposition is always the go-to option for the assist, and for good reason, as she can replace allies over any terrain. But, pivot is also a viable option for a somewhat off-tank tanky-ish unit like her, as she can just move two extra spaces into danger. Any movement command will work too.
Next, the special. Bonfire is for a constant damage of an extra 17(ish, depending on the iv), while Luna is a more risky, more effective on other tanky units, and is a budget option, so Luna is a better choice than Bonfire.
As far as the A slot passive goes, Fury is the best option. Fury 3 goes better for an offensive set or if she is with a healer (or off healer flier) or if she uses seal attack, while Fury 2 is better for a more defensive or average set, or if she utilizes renewal.
Her B slot should be seal atk or renewal. Seal Attack 3 is better for the more offensive set, or even the average set, while Renewal is better for the defensive or average set. Guard 3 is also an ok option for a defensive build only.
Her C slot depends on whether she is in an emblem or not. If she is in a flier emblem, she should have a fortify fliers partner, but her C slot should be Goad Fliers. Goad Fliers is way cheaper than Hone Fliers, and in lots of situations, better. If not in an emblem, attack smoke is used for keeping enemies from killing her.
Her Sacred Seal should be any one of the deflect skills. As she can already take most blue and red and even some green melee units, and can already take lots of blue and red mages, Deflect Missile 3 is the best option. She can already take a death blow 3 atk boon Reinhardt, and live with one hp (after Fury), she cannot take any atk boon LnD Brave archers. Though with Deflect Missile 3, she can take all of them except speed boon LnD 3 sacred seal speed +2 Setsuna, as she can quad this Catria at 37 spd (the average). Though Deflect Magic 3 can be used to take even less damage from mages.