Not to mention that she had a direct order from her Warchief. Even before Sylvanus gave the order, Vol'jin also recognized that things were going to shit.
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Are you kidding me? Why do people try so hard to defend this idiotic story?
Varian commanded Mekkatorque to call in the gunship BEFORE the horde retreated. Which means the airship was on station near the battle. Close enough to see green flares in the middle of a battlefield filled with green crap. Which means it was also close enough to survey the rest of the battlefield.
Give it up already. The entire situation was stupidly presented, and full of cheap contrivances. I'm not even defending the horde's actions. I'm just saying the entire scene was written poorly.