What do you guys think about this Olivia's build?

Pretty awesome. If you're running Brazen, however, I would suggest that you might want to look into using Escape Route in place of WoM. Once she gets within Brazen range, she will be able to teleport to anyone, regardless of their health. Otherwise, she looks really good. Olivia can make use of nearly any build; I run a purely supportive version, a friend has a mixed-tank murder machine with Armorsmasher.

Trade the A slot for brazen attack/speed and then use the flashing blade seal on the s slot in my opinion would improve it more. 41 resistance is a lot for someone who can't attack back. and 34 is plenty to tank a hit if need be.

Aether is kind of counterintuitive when you want her health to stay in the brazen/WoM threshold. If you really still want a high scoring skill you could go galeforce instead, but any quick offensive skill can work too.

I run something similar, I guess?

+Def/-Res
Safeguard (Def)
Dance
Luna
Close Defense
Chill Speed
Attack Tactic
Close Defense Seal

Basically, she dances and is set up to be able to tank any hits from physical on Enemy Phase, with Luna charged for your next turn. I sometime swap out Attack Tactics for Attack Smoke, and Chill Speed for Swordbreaker.