She'd told Ditto of the danger, what'd she seen in her vision. Yet, even now, as they were teleported to Reagan High and into the chaos that awaited them there, Cassandra felt they were incredibly unprepared. 

Kendra didn't know much about the various Lantern corps. However, upon having her vision a couple of days ago, she had taken time to research almost obsessively over the Red Lanterns, who's description somewhat reminded her of the Norse-time Berserkers of old. They had all the powers of the Green Lanterns and more, and fuelled their powers with rage and hate. Their blood, as Toby Garrison was now demonstrating with an unfortunate victim, was now as hot as lava, and the Red Lanterns had the power to regurgitate this blood.

Now, if only Wikipedia had given her some idea about how to stop one. 

Only a few minutes had passed since they had engaged the target, and already things were going mad, with one of their team, Hellfire, turning tail and fleeing. Seeing one of the older, more experienced heroes on the team run away didn't fill Cassandra with much confidence and, for only a minute, she found herself momentarily overwhelmed with a feeling of fear. Just as she was about to turn to Ditto and ask if he had some plan of attack, orders came in... but they weren't from Ditto.

“Supergirl,” Question's shout sounded. “Quit playing the fool and attack the Red Lantern. Only you are strong enough to withstand him! Armory, Starbolt and Miss Mountain, support Supergirl’s attack, avoid a frontal attack while subverting his position. Cassandra, use your power, get the civilians most at risk out of here, Ditto, put some clones at her disposal.”  

A small part of Kendra was shocked at his arrogance for assuming a position of authority. However, she had to agree that this seemed to be the best plan of attack. Snapping herself out of her doubt, ordered her spear into attack mode and made her way over to the panicking civilians. "Supergirl, listen to Question!" she called up to the girl. "I'll take care of the civilians! Your efforts are best served against the Lantern! Go!" Cassandrathen started trying to herd the crowds of students and teachers away from danger. "Go, go! Move!"