It doesn’t really seem like Kumoko is arguing with herself at all. It looks more like confusion and freezing in shock. First, Kumoko gets warned. Next, she looks around, likely to find out where the threat is so she can avoid accidentally running towards it. Next, she learns that the threat is more powerful than the strongest threat they know. Understandably, she is shocked by this. She is about to say something about how there’s no way she can do “something” before getting interrupted in the middle of her sentence. She never provides any counter-arguments or tries to deny the existence of a more powerful being, she’s more just shocked and confused. There’s also a possible reason for her to wait until she sees the incoming threat, what with her Appraisal skill and ability to track other beings. Kumoko might also have thought she’d have more time to talk, and thought that whatever threat was coming wouldn’t come as fast as it did.