Bev just looks around too, and then she looks to Eponine once more. The water is rising, and she knows that if this is a thing that needs to be faced, then the answer isn't going to be up there. So, with her cold fingers fumbling to the sword belt around her waist, Bev just undoes it and offers it to the girl.

"Hold this. I'm going to go down under and see if I can find something that undoes the door."