I think besieging the place is a good idea. Just stand at the entrance of the hall and shrug at Alice. See if she takes any action. They can send one person up to collect food for them; if she has another way out, they'll find out about it and chase her (although it probably is on the far side of the zombies). If she doesn't, she'll be forced to engage.
Also re: missile deflection: "It's magic used to protect the user from any sort of missiles. As long as it's not a ballista, we should be saved with that." - https://mangadex.org/chapter/775049/3
Don't know where you're getting stuff about it not blocking arrows.