Tbh, i can clearly see why she's free.

Picture taken from Natsu Uchiha's thread here:

Mystery: Generates a shield for a selected friendly unit, based on 50% of Samui's resistance. The selected unit will also be immune to low float, high float, repulse and knockdown. Lasts for 2 rounds.

Standard: Attacks a random unit and causes tag. High chance to cause repulse.

Chase: Chases and attacks a knocked down unit, causes low float and tag. Can be triggered twice each round.

Passive: At the beginning of the battle, increases the team's attack by 30%, lasts for 3 rounds (note: the word for 'team' here, literally means 'small team', which is specific to your own lineup, and not across the battlefield).

Addendum (now that i've found it):

Passive 2 (when Samui is upgraded to 3 stars): Before the first action every round, disperses 1 layer of debuffs on all Hidden Cloud ninjas in the team (note: again, the Chinese word for 'team' used implies that it's only effective in your own lineup, and not across the battlefield)

Disclaimer: I did this in a rush, so if anyone spots a mistake, please let me know.

Shameless self-plug: Check my art out uwu i put a lot of time and effort into them! My most recent work, for example, is Breeze Dancer being high-fasion in the summer(or you could just click on my username and look for the posts in the 'Fanart' section )