+Atk -Res P!Olivia

Ouch. Her resistance was actually pretty decent, but because it's -Res, then +Spd refinement is probably your best bet.

As for skills, that's dependent on what you're using her for. While she can be used for damage, she's also a support unit, so dancing is usually the most important thing for her. Fury 3 increases her stats, Wings of Mercy is for support, things like Windsweep can be used to safely attack units without the fear of retaliation, Desperation for more damage.