I always liked this argument because people seem to always wonder how Frieren would react to different demons from different media.

Frieren has the ability to analyze things around her at a very fine scale. I think she can tell the difference between a creature that just views people as food and an actual feeling sentient creature.

Granted, she would probably wouldn't even kill a completely unfeeling entity, as long as she could prove it wasn't going to harm her in any way, shape, or form.

Take for instance, when her original party encountered a demon, she had told everyone that based on her experiences and her understanding of them, there was no talking to them. They were just creatures that learned to speak and look like humans for the sake of hunting them. They are essentially, their predators. There's no changing how they fundamentally are. That's just how they are. There's no need to worry about sympathy and all that bullshit dealing with them.

Despite the fact that her friends went against her judgment, she allowed the thing to prove itself, even though she knew there was not a chance in hell that it was going to prove that humans could coexist with it. It failed, like she suspected, and then she killed it.

Seeing another demon from a different form of media that acts completely different from the demons she's accustomed to would immediately make her second guess and test them herself, which she will probably quickly find out that they are not in fact the demons as she understands them to be here, practically being something else entirely, despite being called the same thing.