Whitewing refines + Desperation + Brash Assault?

BA is only if you're trying to break wary fighter. If you have two goads nearby, which is likely enough for the condition of the brave effect, her spd should be well into the 40s even without merges

Just add +11 to her atk (after weapon mt) and spd IVs and you can start figuring out what you want to do with that.

I would think brash + desp would work better for Est and Palla rather then Catria because she has the highest speed of the sisters. She does have 37 with a spd boon so fury would probably work or you can run brazen atk/spd if you don't have spd boon or hone fliers.

She's pretty easy to build for a team with other fliers. She doesn't have an easy way to get into HP range for the Desperation+Brash Assault combo.

For a PVE build I'd just go for her effect refine and a 2 CD special (reduced to 1), which will always trigger the special on the second hit of the 2 attack sequence assuming the foe doesn't have a guard effect.

You could always peruse Catria's page for some ideas, I made my Catria an Omni Tank - Just hunting that Perfect IV and +10th merge (Hopefully they can both be the next Catria I summon)