I was not endorsing her killing the sisters to prevent the Seanchan from using them, I was approving of her shooting down the enemy's power. Even if they

Not the novices and Accepted. And given all else that has been discovered or recovered, how far are you willing to bet the Seanchan cannot find a way aroud the Oaths, or uses for Aes Sedai that allow more combat-capable damane to go to the front. My own personal opinion is that channelers contribute better to warfare away from the front lines of battles. Granted, the way in which the Seanchan use their damane limits most of the support functions at which channelers can be so useful, but they are the most professional and creative military institution in the known world - they can definitely find uses for the restricted damane.
She did not have the luxury of sparing their lives - they were aboard enemy beasts of burden. The to'raken were legitimate targets, regardless of whether or not they also bore captive initiates. Should she let them fly off with their damane burdens, drop them a a nearby staging camp to be transported overland to the Seanchan, while the to'raken return to the Tower for another damane-strafing run or to snatch more captives? Sucks to be the sisters on board, but the Seanchan and their creatures have to go. Since the to'raken are limited in number (does the Return have any breeding stock with them? Any chicks/pups/whatever being trained to replace their losses? All in all, killing the to'raken is a worthy goal in its own right. Whatever the fliers might think, the unique logistical value of the to'raken far outweighs that of the raken, and they are by far the most valuable of the Seanchan exotic creatures, second only to damane. A chance to kill both on the field of battle MUST be seized when presented. It is simply tough luck for any sisters who plunge to their deaths aboard them.