Fly by Night by Frances Hardinge

In this intriguing middle grade fantasy, twelve year old Mosca Mye leaves town with a con man she has just met and her feisty goose.  Set in the middle ages in a world where guilds rule and all writing is banned unless it is approved by the Stationers guild, Mosca had been taught to read by her now deceased father.  In her journey, she is drawn into the political and religious clashes in the kingdom.