This is a player phase oriented build I like to call "Clair Phase". It takes advantage of her offensive capabilities, particularly on Flier teams, and let's her run amok during Player Phase. She has enough defenses to safely get into Brazen/Desperation range that makes her even more deadly during Player Phase.
This is my mixed phase build. She uses Brazen Def/Res instead here to beef up her defenses but her base stats are pretty similar. Renewal keeps her topped up on HP making it fantastic for Tempest Trials and Chain Challenges and I've done many without having a healer on the team. Iote's Shield allows her to lure in archers safely.
This is my "Mage Counter" build, though it works for dragons too. This is entirely designed to push her Res to stupid levels while also giving her Distant Counter to KO or at least damage mages on her turn. She's practically invincible against magic attacks, especially with Flier buffs, and while her attack power is generally more mediocre (though she will basically ALWAYS proc Def Ploy with this build so that mitigates the issue a bit), her Glacies proc is insane in this build especially on enemy phase, allowing for some opportunistic deletions of problematic enemies.
This is a Def Tank build (though her Res is still high so it's more of a Mixed Tank build), which is ironic considering she's supposed to have naturally low Def and my Clair is +Res, -Def on top of that. However, I manage to push her to 34 base Def which is good enough and Red units won't be a problem for her. However, once the Brazen skill kicks in and you take Flier and Support buffs into account, she actually gets really beefy. On a Flier team focused on buffing her Def, she will hit 57 Def with the proper formation and will also have her Res significantly boosted too.
And then this is the Hit and Run build. It's pretty throwaway and I haven't used it much yet, though I might slap a Firesweep Lance on her and focus more on buffing her Atk and see how it goes.