I think what may happen is that
Lizzy was somehow infected by
Saul (if he is a carrier) hence the vomiting and then she turns while under captivity of
the Mallers.
After a hard fought battle with the Mallers
the tower folk come across a freshly infected Lizzy and Saul is the one to do what has to be done. Sad face.
Maybe even
Scratch and
Bricks join the Tower, they are great
characters.
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