Elizabeth tells the prisoner: "The people are making preparations to leave. I'll return when I figure out how best to free you." She doesn't tell the prisoner they're planning to leave tomorrow.
Elizabeth does what she can to help with preparations, and packs anything important of hers, plus any rare, portable materials/books.
If she has space/time available, she might try to squirrel some of her larger possessions away out of sight in case she can return for them, later. Perhaps there's a hidden spot in her house or where she works.