What is the theme of the novel Lyddie by Katherine Paterson?

There are several themes that are present in Katherine Paterson's Lyddie.

One theme present is slavery.  The theme is introduced early on in the novel when Lyddie comes face to face with Ezekial, a runaway slave.  It is through him that Lyddie sees similarities between his struggle and her struggle.  There are repeated references to slavery throughout the novel.  For example, in Chapter Twelve Betsy makes the comment that she and the other factory girls are treated no better than slaves.  Lyddie adamantly claims that she is not a slave, but as working conditions continue to deteriorate, Lyddie is less and less sure of her opinion.  

Another theme is that of female independence.  In our modern world, audiences are inundated with male hero characters, so Lyddie is a refreshing read.  Not only is the central character a female, but she is a strong, brave, and fiercely independent female.  For example, Lyddie shows incredible courage when she decides to leave Cutler's Tavern to become a factory girl.  She continues to be a laudable character because she continues to show the value of being an independent woman with a high work ethic.  

Lastly, I think there is a theme present that shows the value of education.  Throughout the novel, readers are shown the value that Lyddie and her roommates put on education.  Lyddie learns to read while living with the other girls and challenges herself to continue learning.  Betsy leaves factory work in order to go to Oberlin College, and the novel ends with Lyddie deciding to go to college instead of trying to find work elsewhere or taking Luke up on his marriage proposal.