So the middle ground would not work. This was a problem. A large problem. A large, fast problem that, should they--should she--hesitate, would quite possibly end her participation in this War before it could truly begin. Nervously, she glanced up at the problem in question. She had no doubt that it would be able to catch up to her should she attempt to run, or should Saber attempt to carry her. Retreating on her own while her Servant held the thing off was a gamble, a Hail Mary. It could work, but she had no way to be sure that it would. Given that it had an aerial advantage, it would most likely just find a way to go over Saber to her.
As for their other option... Marguerite had no doubt that should Siegfried use his Noble Phantasm, he would be able to destroy the giant insect, or at least drive it off. If it didn't, they were likely already dead. But was that a risk she was willing to take? Would she take such a drain on her prana? Would she reveal her Servant's identity and thus his legendary and obvious weakness this early in the War? She had no idea who if anyone was watching at the moment, but she was sure the act would not go unnoticed. It was entirely possible that by winning this battle, she would lose the War.
This was bad. This was very bad. So bad she regretted deciding to come out in the first place. But there was no time for regrets. She had to make a decision, and fast.
"Saber... Drive it off." Marguerite Calder stood straight, voice commanding, every inch a magus, every inch a Master. She could second-guess her decision later, but for now she needed to show unwavering resolve.
"Use your Noble Phantasm."