I could see your point if Queluna was blocking the door. The monster would have to really work to get past her to Amelia. She's not, though. The monster is. The monster just has to step forward and brush the elf aside, or just try and smash Amelia from there, even. He's got a lot of reach. Queluna isn't an immovable object, after all. If the monster wants to get around her and focus on something else, it will.