I Got Elincia hp+ def- but what build shoul i give her?

She really doesn't need much to help her shine. Death Blow, or Swift Sparrow if you want to go for a quad build. She's got enough bulk and speed to usually survive one hit and avoid a double, so it wouldn't be tough to get her into desperation range, and if she's got at least 2 allies with Goad Fliers(fairly easily available, too) she will quad a LOT of enemies. You might want to give this a try(built in unit builder.) but you could also swap in Fury if you want to Desperation easier.

this is my elincia, she's -atk +def so I gave her lnd but I guess if ur -def for her A slot u can go deathblow / swift sparrow instead