/kicks her boss while we're at this!
[Her focus is entirely on the black woman, determining which way the unknown Servant will attack. Saber is an offensive fighter by nature, so defending another puts her at a slight disadvantage-- but the sword and confidence of the King of Knights will not be shaken quite so easily by mere circumstances, or an unknown opponent.
But yet another happens into the confrontation, that she spares only a glance for, frustration now beginning to seep into her as things grow complicated]
Stay back! This woman is dangerous! [Not a panicked warning to the young girl, but an order she is so used to giving. So long as that one doesn't try anything foolish, the situation can still be salvaged. But it's already at the point where even Saber is starting to worry about the outcome, enough so that she addresses the dark Servant once more, with a last ditch attempt at diplomacy]
I cannot do that. I ask that you retreat, else I will be forced to cut you down.