The phrase "She had not even a ‘white bone in her mouth,’ while the rest of the fleet had whole skeletons" is likely a metaphorical expression used to describe a situation where someone or something lacks the usual signs of strength or success that others possess.
In this context, the writer may be referring to a person or entity that lacks the resources, abilities, or advantages that others in their group possess. The "white bone" is a symbol of strength and completeness, and by not having it, the subject is seen as weak or incomplete. Meanwhile, the "whole skeletons" are the other members of the group who possess this strength.