I mean she could have gotten Ray to just absorb/eat all their metal stuff, but no they have to forget something so important because the MC has to go through something for story and that'd be too anticlimactic.
@Isekailoverrr She wasn't in the right state of mind. She was both scared and angry, and the first thing that came out of her mouth was revenge. Once she realized what that meant after hearing that guy's arm get pulverized and hearing his screams did her head clear a bit. By that point it was moot, especially since he lost his head soon after she told Ray to stop anyway. I still agree, though. Woulda been better if she had him eat all their metal. But can you say for certain that you'd be able to think of the most efficient way to dissolve a situation when you're bombarded by dread and anguish?
Uhm pretty sure she didn't ask Ray to eat their weapons because Ray is supposed to be a regular pet snake, not a metal-eating spirit. She probably wants to keep that fact hidden.