+SPD or +ATK combat dancer Oliva?

I think +Speed might be a more important stat for her.

What weapon are you giving her, Ruby Sword+?

Easily +Spd

Definitely +spd. I've only pulled a +atk, and she works well, but she would like a little more speed.

+Atk can work fine, but +Spd helps more

As a general rule of thumb, dancers want +spd.

Any IV set is serviceable, but +spd is the best one. They're usually all fast, and with a boon in speed they usually break into a higher tier which means more doubles caused, and less doubles suffered.