Cowardism... :uhoh: fear of fighting Cassandra 1 vs 1... :uhoh: I think you totally misunderstand just how evil Roxanne is and her motives. It wasn't fear that caused her to do this, it was her vindictive nature.
I believe that Roxanne's reasoning for setting the stage up so Cassandra would fight her in front of all the other warriors, was to humiliate her then let them reject her by joining her side against Cassandra. She wasn't scare of attacking her at all... what she wanted to mess with her head as much as possible is what it boiled down to.
Look, Cassandra viewed her move as disgusting and was ashamed of the technique, so Roxanne attacked that aspect of her personality. First she removed the only warrior whom had accepted her and her technique, this scoring the double victory of being the trigger for Cassandra to attack everyone to get to her. Then Roxanne set up a situation back at org HQ where Cassandra would be forced to use the technique she was ashamed of in front of everyone in order to totally humiliate her by making her reveal her vial technique before she killed her. That is why Roxanne personally antagonized her about #35 enjoying her horrible death and then was shouting how odd and ungraceful the move was. Both to point out to Cassandra what she had just down, whom she revealed the technique too, and to drive the warriors into a frenzy to attack her. However since Cassandra's greatest fear was rejection, after Roxanne stopped her movements she let the other warriors finish her off slowly and painfully just to add further insult to injury. That way she'd feel utterly rejected by her fellow warriors at the end, deprived of vengeance, and ashamed of harming her fellow warrior all at once... while slowly dying over several hours in agony.
Roxanne was aiming to torment Cassandra and then kill her once done, not protect herself by hiding behind other warriors. Roxanne is more twisted than you realize... and totally evil and beyond redemption. She truly is a villain you love to hate... well assuming you aren't messed up like me anyhow

:, then you cheer her on wanting to see what other conflict she'll add to the plot before she dies.

:eyespin:
Think of it like this, Roxanne is that mean & vindictive girl at school but with endless power, plenty of brains, and nothing else to do besides attacking your very being then killing you once she's done. She may have been a coward in the past and still maybe but in that moment cowardism wasn't her motivation. At best she liked the idea of watching more than doing in this case and at worst she considered the protection a bonus to her plan... but her motivation was to torment poor Cassandra, nothing else.